••.:,'.-...•..,...•. 


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PREFACE 

THE  scope  and  purpose  of  this  book  are  'indicated  in  the  title. 
It  is  intended  to  give  the  student  such  assistance  as  can  be 
obtained  from  books  in  acquiring  a  knowledge  of  those  funda- 
mental facts  and  general .  principles  of  chemistry  upon  which 
the  superstructure  of  agricultural  chemistry  or  other  technical 
application  must  necessarily  rest.  Though  many  excellent 
works  on  chemistry  have  been  published  in  recent  years,  few, 
if  any,  have  been  expressly  designed  to  meet,  or  are  exactly 
suited  to,  the  requirements  of  this  large  and  increasing  class 
of  students. 

In  the  present  volume  the  authors  have  attempted  to 
emphasise  those  aspects  of  the  subject  which  are  of  special 
importance  to  such  students,  while  others  have  been  treated 
in  sufficient  detail  to  enable  the  general  principles  to  be 
securely  grasped.  In  order  to  avoid  the  mischievous  tabula- 
tion of  disconnected  facts,  matters  of  purely  technical  interest 
have  been  as  far  as  possible  omitted  from  the  text;  but 
numerous  footnotes  have  been  added,  pointing  out  the 
application  of  the  general  principles  to  commercial  and 
industrial  processes.  These  notes  should  add  to  the  interest 
of  the  work  and,  to  a  certain  extent,  give  point  to  the  students' 
reading. 

The  arrangement  of  the  matter  is  perhaps  somewhat 
unconventional.  The  underlying  idea  is  to  take  advantage 
of  that  which  the  student  already  knows  regarding  the 
common  things  of  life,  the  things  with  which  every  one  is  more 
or  less  familiar,  to  formulate  this  knowledge,  extend  it,  and 

357292 


vi  PREFACE 

incorporate  the  whole  in  a  homogeneous  system.  The  plan 
is  based  upon  courses  of  lectures  given  by  the  authors  during 
a  period  extending  over  many  years.  They  believe  it  to  be 
theoretically  sound ;  and  in  practice  it  has  proved  efficacious. 

The  phraseology  employed  is  the  simplest  that  could  be 
used  consistently  with  accuracy  and  clearness,  and  all  technical 
terms  are  fully  explained.  It  is  hoped  that  the  book  will 
prove  useful  to  students  attending  "  short  courses "  in 
agriculture,  horticulture  and  dairying,  as  well  as  to  those 
preparing  for  College  and  other  diplomas,  in  these  subjects, 
e.g.  the  N.D.A.,  N.D.D.,  also  to  those  who  are  attending 
education  courses  in  hygiene  and  domestic  economy,  and  in 
fact  to  all  who  take  up  the  study  of  chemistry  as  a  preliminary 
to  some  technical  or  commercial  pursuit. 

At  the  end  of  the  book  is  placed  a  selection  of  questions 
and  problems.  These  of  course  are  not  exhaustive,  but  are 
intended  to  fix  the  attention  of  the  student  upon  those  portions 
of  his  work  which  are  of  fundamental  importance. 

READING 

December,  1912 


TABLE    OF    CONTENTS 

CHAPTER   I 
MATTER  AND  ENERGY 

PAGE 

Nature   and   Relationship   of  Matter  and   Energy  —  Physical   and 

Chemical  Change — Elements,  Compounds,  and  Mixtures     .     ,         I 

CHAPTER   II 

;  AIR 

A  Mixture  of  Oxygen  and  Nitrogen — Other  Constituents — Solubility 
— A  typical  Gas — Properties  of  Gases — Temperature  and  Pres- 
sure— Correction  of  Volume  .  7 

CHAPTER   III 
THE  CHIEF  GASES  OF  THE  ATMOSPHERE 

Oxygen — Combustion — Respiration — Oxidation  and  Reduction — 
Oxides — Preparation  of  Oxygen — Commercial  Oxygen — Ozone 
— Nitrogen — Occurrence,  Properties,  and  Preparation  ...  15 

CHAPTER   IV 
WATER 

Natural  Waters — Impurities —  Filtration — Distillation —  Physical 
Properties — Solvent  Action — Crystallisation — Drinking  Waters 
— Chemical  Composition ,  ,  33 


viii  TABLE   OF   CONTENTS 

CHAPTER   V 
HYDROGEN 

PAGE 

Preparation — Physical  Properties — Chemical  Properties  ....       32 

CHAPTER  VI 
GENERAL  PRINCIPLES 

Nomenclature — Symbolic  Notation — Laws  of  Chemical  Combination 
—  Atomic  Theory  —  Formulae  and  Equations  —  Valency  — 
Calculation  of  Quantities  by  Weight  and  Volume 37 

CHAPTER  VII 

OXIDES,   ACIDS,   BASES,  AND  SALTS 

Characteristic  Properties  of  Acids  and  Bases — Salts — Monobasic  and 
Dibasic  Acids — Normal,  Neutral,  Acid,  and  Basic  Salts — 
Peroxides — Electrolysis  and  Ionic  Dissociation 53 

CHAPTER  VIII 
LIMESTONE 

Chalk,  Limestone,  and  Marble — Occurrence — Formation — Lime- 
burning  —  Quick-lime  —  Slaked  Lime  —  Mortar  —  Portland 
Cement — Calcium  Salts — Carbide — Carbon  Dioxide — Hardness 
of  Water — Commercial  Carbon  Dioxide — Ventilation  ...  64 


CHAPTER   IX 
COMMON  SALT 

Occurrence — Uses  —  Physical  Properties — Hydrogen  Chloride  — 
Avogadro's  Hypothesis  —  Chlorine  —  Bleaching  —  Bleaching 
Powder — Other  Halogens — Sodium — Sodium  Salts  ,  ,  ,  ,  73 


TABLE   OF   CONTENTS  ix 

CHAPTER   X 
SULPHUR 

PAGE 

Occurrence  —  Physical  Properties  —  Varieties  —  Sulphur  Dioxide  — 
Sulphurous  Acid  —  Sulphites  —  Sulphur  Trioxide  —  Sulphuric 
Acid — Sulphates — Hydrogen  Sulphide — Allotropy  ....  83 

CHAPTER   XI 

ASHES 

Wood  Ashes — Potassium  Carbonate — Potassium — Potassium  Salts — 
Bone  Ash  —  Calcium  Phosphate — Phosphorus  —  Phosphorus 
Pentoxide — Phosphoric  Acid — Orthophosphates —  Superphos- 
phate— Other  Oxides  and  Hydroxides  of  Phosphorus  •  •  •  95 

CHAPTER  XII 
SAND,  CLAY,   ETC. 

Nature  of  Sand  and  Clay— Silica— Water  Glass— Dialysis— Colloids 
— Osmosis — Silicic  Acids — Silicates — Kaolin— Plastic  Clay — 
Bricks  and  Pottery — Glass — Hydrogen  Fluoride — Action  on 
Silicates — Boron— Borax  ...  105 


CHAPTER  XIII 
ORGANIC  MATTER 

Combustible  Portion  —  Destructive  Distillation  —  Wood  Charcoal 
—Bone  Charcoal  —  Coal  —  Coke  —  Coal  Gas  — Gas  Tar  — 
Carbon — Graphite — Diamond — Carbon  Monoxide — Ammonia — 
Ammonium  Hydroxide  —  Ammonium  Salts  —  Putrefaction  — 
Nitrification — Composts — Nitrates — Occurrence  in  Nature — 
Manufacture — Fixation  of  Atmospheric  Nitrogen — Nitric  Acid 
—Oxides  of  Nitrogen "7 


x  TABLE  OF   CONTENTS 

CHAPTER   XIV 
PARAFFINS  AND  THEIR  DERIVATIVES 

TACK 

Marsh  Gas — Crude  Petroleum — Commercial  Products — Fuels,  I^amp 
Oils,  Lubricants,  Vaseline,  Paraffin  Wax  —  Hydrocarbons — 
Substitution  Products  —  Alcohols  —  Aldehydes  —  Acids  —  Un- 
saturated  Compounds  —  Ethers  —  Polyhydric  Alcohols  —  Fats 
and  Oils — Soaps — Isomerism — Carbohydrates — Fermentation — 
Dibasic  Acids— Hydroxy  Acids— Nitrogenous  Compounds  .  .  139 

CHAPTER  XV 
COAL  TAR 

Distillation    Products— Benzene — Phenol— Derivatives — Comparison 

with  Fatty  Compounds 187 

CHAPTER   XVI 
SOME  COMMON   METALS 

Alkalis — Earths — Aluminium— Heavy   Metals— Iron — Manganese — 

Zinc— Copper— Lead— Noble  Metals— Arsenic— Tin— Alloys   .     192 

ATOMIC  WEIGHTS 217 


APPENDIX 

WEIGHTS,  MEASURES,  ETC  ............  218 

QUESTIONS  .................  219 

EXAMPLES  FOR  CALCULATION    .          .........  232 


INDEX 
ANSWERS 


A    FOUNDATION    COURSE    IN 

CHEMISTRY 

FOR    STUDENTS   OF  AGRICULTURE   AND 
TECHNOLOGY 

CHAPTER   I 

MATTER    AND    ENERGY 

THE  systematic  study  of  the  physical  universe  which  we  call 
"  Natural  Science "  deals  with  two  things,  "  Matter "  and 
"  Energy." 

Matter. — Matter  may  be  defined  with  sufficient  accuracy 
for  our  requirements  as  that  which  occupies  space.  It  comprises 
everything  which  can  be  touched,  handled,  weighed,  or  seen — 
all  things  around  us,  our  own  bodies  included,  and  of -the 
existence  of  which  we  become  aware  by  means  of  our 
senses. 

Each  kind  of  matter  has  certain  properties  of  its  own 
which  distinguish  it  from  other  kinds  of  matter.  Some  sub- 
stances under  ordinary  conditions  are  liquid,  others  gaseous, 
many  solid.  Some  melt  easily,  others  can  only  with  difficulty 
be  made  liquid.  Some  give  off  odours,  others  affect  our  sense 
of  taste ;  and  it  is  by  recognition  of  these  properties,  or  of 
differences  in  colour,  texture,  density,  etc.,  that  we  generally 
distinguish  one  kind  of  matter  from  another. 

Energy. — The  idea  of  Energy  or  the  power  of  doing 

B 


2      A    FOUNDATION    COURSE   IN   CHEMISTRY 

mechanical  work,  is,  perhaps,  not  quite  so  familiar.1  Matter 
and  Energy  are,  however,  equally  real,  so  real  in  fact  that 
we  are  continually  purchasing  both.  We  buy  iron,  bricks, 
or  other  building  material.  We  also  buy  coal ;  but  we  only 
need  that  substance  that  we  may  burn  it,  and  so  liberate  the 
form  of  energy  which  we  know  as  heat,  and  with  which  we 
may  cause  work  to  be  done.  We  could  dispense  with  the 
coal  if  other  forms  of  energy  were  at  our  disposal.  In 
districts  where  there  are  waterfalls,  the  energy  of  the  falling 
water  is  largely  used  for  doing  work  which  in  other  places 
is  performed  by  burning  fuel. 

Energy  differs  from  matter  in  that  any  one  form  may  be 
changed  directly  or  indirectly  into  any  other  form.  Thus,  in 
an  electric  power  station,  when  coal  is  burnt  in  the  furnaces 
and  heat  thereby  produced,  this  form  of  energy  is  successively 
converted  into  motion  of  the  machinery,  energy  of  the  electric 
current,  motion  of  the  tram-cars,  and,  it  may  be,  light  for 
illumination.  Heat,  light,  sound,  motion,  are  all  manifestations 
of  energy. 

Physical  Change.— Matter  can  exist  in  three  states,  solid, 
liquid,  and  gaseous,  and  many  substances  may  be  made  to 
assume  each  of  these  states  successively,  generally  by  the 
action  of  heat.  The  substance  which  we  know  as  ice,  when 
heat  is  applied  to  it,  does  not  become  hot,  it  merely  melts, 
and  this  change  of  state  represents  the  work  which  the  heat 
has  done;  the  liquid  formed  is  water,  and  this  on  further 
application  of  heat  becomes  hot,  i.e.  its  temperature  is  raised. 
After  a  while  it  boils  and  is  converted  into  steam,  the  gaseous 

1  Treatises  on  Mechanics  give  detailed  information  in  regard  to 
Energy,  Force,  Work,  etc.  The  following  definitions  should  be  kept  in 
mind  : — 

Force. — That  which  produces,  or  tends  to  produce,  motion  in  matter. 
Work. — A  force  is  said  to  do  work  when  it  moves  its  point  of  applica- 
tion.    It  is  measured  by  the  product  of  the  force  into  the  distance  through 
which  its  point  of  application  is  moved. 

Energy. — The  power  of  doing  Mechanical  Work.  There  are  two 
kinds  of  Energy  :  Kinetic,  due  to  motion,  and  Potential,  due  to 
"position." 

Mass. — The  quantity  of  matter  in  a  body  (a  constant). 
Weight. — The  force  with  which  the  earth  attracts  a  body  (a  quantity 
which  varies  at  different  parts  of  the  earth's  surface). 


MATTER   AND   ENERGY  3 

form  of  water.  By  the  application  of  heat  to  ice  and  water 
we  have  caused  successive  changes  of  state,  but  the  com- 
position of  the  substance  has  remained  unaltered,  nothing  has 
been  taken  out  and  nothing  put  in.  A  change  of  state  is  a 
physical  change. 

When  a  piece  of  vulcanite,  such  as  the  handle  of  a  fountain- 
pen,  is  rubbed  vigorously  on  woollen  material  it  acquires  the 
property  of  attracting  light  bodies — dust  particles,  small  pieces 
of  paper,  etc. — and  is  said  to  be  electrified.  When  an  electric 
current  is  passed  along  a  wire  coiled  round  a  steel  bar,  the 
bar  becomes  capable  of  picking  up  other  pieces  of  steel  or 
iron,  and  if  suspended  horizontally  always  sets  with  one  end 
pointing  towards  the  south  and  the  other  towards  the  north. 
It  is  said  to  be  magnetised.  Both  of  these  changes  are 
physical.  The  composition  of  the  vulcanite  has  not  been 
altered,  and  analysis  can  detect  no  difference  between  magne- 
tised and  unmagnetised  steel.  The  substances  have  obviously 
undergone  some  modifications  in  their  properties,  but  these 
modifications  have  not  be$n  accompanied  by  any  change  in 
composition. 

Chemical  Change. — If  we  mix  some  of  the  yellow  fusible 
solid  known  as  sulphur,  with  about  an  equal  quantity  of  fine 
iron  filings,  they  form  together  a  greenish  powder  from  which 
the  iron  can  be  extracted  with  a  magnet  and  the  sulphur 
removed  by  a  suitable  solvent ;  but  if  we  place  the  mixture  in 
a  glass  test-tube  and  apply  heat  so  as  to  melt  and  boil  the 
sulphur,  a  very  vigorous  action  takes  place.  The  mixture 
becomes  red  hot  and  continues  to  glow  even  when  removed 
from  the  flame.  .After  the  action  has  finished  there  is  in  the 
test-tube  a  new  substance,  a  grey-black  brittle  solid  from 
which  the  solvent  previously  used  will  not  extract  the  sulphur, 
nor  a  magnet  the  iron. 

This  is  a  change  of  composition.  Two  substances  have  so 
acted  upon  one  another  as  to  form  a  third  totally  different 
from  either  of  the  others  in  its  properties,  but  which  can  be 
shown  to  contain  them  both.  This  is  not  a  physical  but  a 
chemical  change,  and  is  called  Combination. 

As    another  instance  of    such  a  change,   consider  what 


4      A   FOUNDATION   COURSE    IN    CHEMISTRY 

happens  when  quick-lime  is  used  for  the  purpose  of  making 
mortar.  Water  is  first  thrown  upon  the  hard  lumps  of  quick- 
lime, which  after  a  short  time  commence  to  swell,  and  then  to 
break  into  a  fine  powder.  At  the  same  time  a  large  amount 
of  heat  is  evolved,  volumes  of  steam  are  given  off,  and  there  is 
ultimately  left  a  dry  powder — if  the  water  used  has  not  been 
too  large  in  quantity — occupying  a  larger  space  than  the 
original  quick-lime,  differing  from  it  in  its  properties  and 
weighing  considerably  more.  The  quick-lime  has  combined 
with  the  water  and  formed  another  substance;  this  product  is 
known  as  slaked  lime. 

It  is  important  to  notice  the  evolution  of  heat  both  in  the 
slaking  of  lime  and  in  the  action  of  iron  on  sulphur,  as  this  is  a 
very  common  accompaniment  to  chemical  combination. 

Again,  take  the  red  powder  known  as  red-lead  or  minium  ; 
when  strongly  heated  it  becomes  yellow  in  colour,  and  a  gas 
which  causes  a  glowing  splinter  of  wood  to  burst  into  flame  is 
given  off.  This  change  is  the  reverse  of  the  two  previously 
mentioned.  The  substance,  red-lead,  has  split  into  two 
simpler  substances,  one  gaseous,  the  other  a  yellow  solid.  This 
is  also  a  chemical  change  but  of  the  kind  known  as  decom- 
position. 

Decomposition  also  takes  place  when  chalk  or  limestome  is 
heated  very  strongly.  A  gas  which  will  extinguish  flame  is 
then  given  off,  and  a  white  solid — quick-lime—is  left. 

Properties  such  as  hardness,  density,  malleability,  fusibility, 
elasticity,  and  capacity  for  being  electrified  or  magnetised  are 
generally  referred  to  as  the  physical  properties  of  a  body,  in 
distinction  from  its  chemical  properties  which  are  manifested 
by  its  power  of  uniting  with  other  bodies,  or  in  any  way  under- 
going change  of  composition. 

The  two  classes  of  changes  which  have  been  described,  and 
which  are  known  respectively  as  physical  and  chemical  changes, 
may  be  briefly  differentiated  as  follows :  chemical  changes 
affect  the  composition  of  a  body,  physical  changes  do  not. 
The  latter  involve  a  change  in  the  energy  content  only. 

Chemistry  deals  with  chemical  changes,  the  means  of 
producing  and  controlling  them,  the  proportions  in  which 


MATTER   AND   ENERGY  5 

substances  take  part  in  them,  and  the  nature  and  properties 
of  the  products. 

Chemical  changes  are  not  unfamiliar  to  us.  Burning, 
rusting,  decay,  are  instances  which  we  see  daily;  and  the 
phenomena  of  life  and  growth  also  involve  chemical  changes 
of  a  very  complex  nature.  No  one,  therefore,  can  be  entirely 
ignorant  of  chemistry,  whether  he  has  studied  the  subject  or 
not.  Recognition  of  this  will  materially  help  to  simplify  the 
earlier  stages  of  the  study. 

Elements  and  Compounds. — Substances  which  can  be  de- 
composed are  called  compounds.  Those  which  have  not 
been  decomposed  are  called  elements.  Every  pure  substance 
belongs  to  one  of  these  great  groups.  Some  eighty  different 
elements  are  known,  but  only  about  twenty  are  of  common 
occurrence,  and  of  the  remainder  some  are  very  rare. 

Iron  and  sulphur  are  elements :  the  substance  formed 
when  they  are  heated  together  is  a  compound.  Red-lead  and 
chalk  are  compounds ;  they  can  be  decomposed  into"  simpler 
substances.  The  familiar  substances,  water,  salt,  sugar,  are 
also  compounds. 

It  is  most  important  to  remember  that  .each  compound, 
although  it  can  be  split  up  into  simpler  compounds  or  even 
into  elements,  is  not  two  or  more  substances  but  one  only. 

Compounds  must  be  clearly  distinguished  from  mixtures. 

When  iron  and  sulphur  are  mixed  together,  each  retains  its 
own  physical  and  chemical  properties,  and  can  easily  be 
separated  from  the  other.  It  is  not  until  the  mixture  is  heated 
that  the  compound  is  formed.  Previous  to  heating  there  were 
two  elementary  substances,  afterwards  but  one  compound  sub- 
stance. The  components  of  mixtures  can  often  be  separated 
by  taking  advantage  of  their  different  physical  properties. 
Thus,  if  sand  and  sugar  are  mixed  together,  the  sugar  may  be 
separated  from  the  sand  by  its  solubility  in  water,  for  sand  is 
insoluble.  A  magnet  could  be  used  to  extract  the  iron  from 
a  mixture  of  iron  and  copper  filings,  since  copper  is  not 
attracted  by  a  magnet.  If  a  mixture  of  iodine  and  charcoal 
were  gently  heated,  the  iodine  would  turn  into  vapour,  and 
could  thus  be  removed  from  the  charcoal  which  would  remain 


6      A   FOUNDATION   COURSE   IN   CHEMISTRY 

unchanged.  Separation  is  not  always  so  easily  performed  as 
in  the  instances  just  given ;  in  some  cases  complicated 
processes  are  necessary,  but  the  method  of  procedure  always 
depends  upon  the  fact  that  each  substance  retains  its  own 
specific  properties. 

There  is  another  and  even  more  important  difference  between 
mixtures  and  compounds.  We  may  mix  together  two  or  more 
substances  in  any  proportions  we  please,  but  the  amounts  which 
enter  into  chemical  combination  are  entirely  beyond  our  con- 
trol. Thus,  seven  parts  by  weight  of  iron  unite  with  four 
parts  by  weight  of  sulphur,  and  twenty-eight  parts  by  weight  of 
quick-lime  with  nine  of  water.  If  we  add  more  of  any  one, 
the  excess  of  that  one  remains  uncombined. 

There  are  other  forms  of  chemical  action  besides  combina- 
tion and  decomposition,^., " double  decomposition,"  in  which 
two  compounds  act  upon  each  other  exchanging  parts  and  pro- 
ducing two  new  compounds ;  and  "  rearrangement "  of  elements 
in  which  a  compound  undergoes  change  within  itself,  and  forms 
a  new  compound  containing  the  same  elements  as  the  original 
compound,  and  in  the  same  proportion,  but  combined  in  a 
different  way.  It  is  unnecessary  to  give  examples  at  this 
stage,  as  many  instances  will  arise  later. 


CHAPTER   II 

AIR 

Nature  and  Composition. — Air  is  a  kind  of  matter.  It 
occupies  space.  As  no  two  bodies  can,  simultaneously,  occupy 
the  same  space,  if  a  vessel  be  full  of  air,  and  it  is  required 
to  fill  it  with  liquid,  it  is  necessary  to  provide  some  means 
for  the  air  to  escape. 

The  existence  of  the  air  is  made  plain  to  us,  although  we 
cannot  see,  smell,  or  taste  it,  chiefly  by  the  resistance  it  offers 
to  the  passage  of  bodies  through  it.  This  resistance  becomes 
much  more  appreciable  when  the  air  is  in  motion  (wind). 

Air  forms  a  gaseous  envelope  around  the  earth.  It  extends 
to  a  height  of  many  miles,  gradually  decreasing  in  density  and 
altering  in  composition.  It  is  impossible  to  state  its  extreme 
limits  with  any  accuracy.  This  envelope  of  air  is  called  the 
atmosphere.1 

Air  can  be  weighed.  A  method  which  gives  fairly  accurate 
results  is  as  follows  :  a  flask  of  about  one  litre  capacity 
(Fig.  i)  is  fitted  with  a  perforated  rubber  stopper  through 
which  passes  a  piece  of  glass  tubing  about  3  inches  in  length. 
To  the  end  of  this  is  attached  a  short  piece  of  rubber  tubing. 
A  mark,  B,  is  made  on  the  neck  of  the  flask,  to  indicate  the 
end  of  the  stopper  and  the  volume  of  the  flask  determined  by 
measuring  the  quantity  of  water  required  to  fill  it  up  to  B. 
About  100  c.c.  of  water,  C,  is  then  placed  in  the  flask,  the 
stopper  with  its  fittings  is  inserted,  and  the  whole  apparatus 

1  Gk.  OT/XOS,  air ;  <r<j>aipa,  a  sphere. 


8      A   FOUNDATION   COURSE   IN   CHEMISTRY 


supported  over  a  bunsen  flame.  After  a  while  the  water  boils, 
and  the  steam  produced  fills  the  flask,  completely  driving  out 
all  the  air.  While  the  water  is  still  boiling,  the  india-rubber 
tube  is  tightly  closed  by  a  spring  clamp,  and  the  bunsen  burner 
immediately  removed.  The  apparatus  is  allowed  to  cool  to 
the  temperature  of  the  room,  and  is  then  weighed.  The  weight 
obtained  is  that  of  the  flask  and  the  water,  but  without  air. 
The  clamp  is  then  opened  and  air  can  be  heard  to  rush  in. 
The  apparatus  is  again  weighed,  and  is  found  to  be  heavier.  The 
difference  in  weight  is  due  to  the  air  which  has  entered. 
The  volume  of  the  remaining  water  must  be  deducted  from  the 
,  A^  whole  contents  of  the  flask,  in  order 

to  ascertain  what  volume  of  air 
caused  the  increase  in  weight.  From 
the  results  obtained,  it  is  easy  to 
calculate  the  weight  of  any  volume 
of  air.  Certain  corrections  for  tem- 
perature, pressure,  and  presence  of 
aqueous  vapour  have  to  be  made. 
The  general  methods  of  making  these 
corrections  are  given  on  page  13. 
One  litre  of  dry  air  at  760  mm. 
pressure  and  o°  C.  weighs  1*293 
grams. 

Air  is  an  excellent  example  of 
a  gaseous  body.  Therefore,  after 
having  studied  some  of  its  properties 

and  discovered  its  composition,  we  shall  use  it  for  investigating 
the  general  properties  of  gases. 

Is  air  an  element,  a  compound,  or  a  mixture  ?  If  we 
place  a  piece  of  phosphorus  in  a  stoppered  bell-jar  over  water, 
set  fire  to  the  phosphorus  by  touching  it  with  a  hot  wire  and 
quickly  insert  the  stopper,  we  shall  see  dense  white  fumes  given 
off  from  the  burning  phosphorus.  When  the  phosphorus  ceases 
to  burn,  the  white  fumes  slowly  clear  away,  and  as  the  contents 
of  the  jar  become  cool,  the  water  rises  considerably  above  its 
original  level,  showing  that  part  of  the  air  has  been  removed. 
The  volume  of  the  air  which  remains  is  about  f  of  the  original, 


FIG.  i. 


AIR  9 

and  it  is  impossible  to  burn  anything  in  this  residual  gas.  By 
burning  the  phosphorus  we  have  removed  that  part  of  the  air 
which  supports  combustion  (p.  16). 

If  we  now  add  blue  litmus  (a  vegetable  colouring  matter) 
to  the  water  it  is  reddened.  The  change  of  colour  is  charac- 
teristic of  a  class  of  bodies  known  as  acids  (p.  53).  It  can  be 
shown  that  the  water  has  acquired  this  property  by  the  solution 
of  the  white  fumes. 

A  modification  of  the  experiment  has  been  used  to  obtain 
and  examine  that  part  of  the  air  which  is  removed  by  burning 
substances  in  it.  If  the  liquid  metal,  mercury,  be  heated 
gently  for  a  long  time  it  becomes  covered  with  a  red  powder ; 
at  the  same  time  the  air  decreases  in  volume  until,  as  before, 
about  4  is  removed.  If  the  red  powder  is  separated  and 
heated  strongly,  it  gives  off  a  colourless  gas  the  volume  of 
which  is  exactly  equal  to  the  amount  of  air  removed  during 
the  heating  of  the  mercury.  If  we  put  a  glowing  splinter  of 
wood  into  this  gas,  the  wood  bursts  into  flame. 

Air  therefore  contains  two  gases,  one  (i  of  the  total  volume) 
in  which  a  taper  burns  vigorously,  and  another  (|  of  the  volume) 
which  extinguishes  flame.  The  name  given  to  the  first  gas  is 
Oxygen  (p.  15),  the  second  is  known  as  Nitrogen  (p.  21). 
Neither  of  these  gases  has  ever  been  split  into  simpler  sub- 
stances. They  are  elements.  More  exact  analyses  of  air 
show  that  the  proportions  by  volume  are — nitrogen,  79  per 
cent. ;  oxygen,  2 1  per  cent. 

Air  is  neutral  to  litmus  and  slightly  soluble  in  water.  Like 
all  gases  it  is  more  soluble  in  cold  water  than  in  hot,  in  boiling 
water  it  is  practically  insoluble.  If,  therefore,  water  which  has 
been  in  contact  with  air  for  some  time  is  boiled,  the  dissolved 
gas  is  driven  off  and  may  be  collected.  When  this  gas  is 
examined  it  is  found  to  be  richer  in  oxygen  than  ordinary  air. 
This  is  strong  evidence  that  in  the  air  there  are  two  substances 
each  retaining  its  own  physical  properties. 

The  same  conclusion  is  arrived  at  from  the  behaviour  of 
liquefied  air.  When  this  is  allowed  to  evaporate  freely,  the 
nitrogen  boils  away  first,  leaving  a  liquid  very  rich  in  oxygen. 

Air  is,  therefore,  not  a  compound  of  oxygen  and  nitrogen, 


io    A   FOUNDATION   COURSE   IN  CHEMISTRY 

but  a  mixture  of  these  elements.  An  additional  proof  is 
obtained  by  mixing  oxygen  and  nitrogen  in  the  proportions  in 
which  they  are  present  in  air ;  there  are  no  signs  of  chemical 
action,  such  as  evolution  of  heat  or  change  of  volume,  and  the 
mixture  is  in  every  respect  similar  to  air. 

There  are  other  substances  in  air  besides  oxygen  and 
nitrogen  ;  the  most  important  are  water  vapour,  carbon  dioxide, 
ammonia,  and  sometimes  nitric  acid  and  compounds  of 
sulphur,  also  dust  particles,  various  kinds  of  bacteria,  and  other 
microscopic  organisms.  It  has  been  found  that  the  nitrogen 
separated  from  air  is  mixed  with  several  other  gases  even 
less  active  than  itself;  but  these  occur  in  very  small  quantities 
and,  for  the  present,  may  be  ignored.  The  amount  of  water 
vapour  varies  considerably.  It  is  generally  greater  when  the 
air  is  warm,  so  that  in  summer  the  air  contains  more  than  in 
winter.  Carbon  dioxide  (p.  68)  occurs  to  the  extent  of  about 
4  volumes  in  1 0,000,  i.e.  0*04  per  cent.  It  must  not  be  looked 
upon  as  an  impurity.  It  is  an  essential  constituent  of  air 
although  the  amount  is  so  small,  and  plants  depend  upon  it 
for  their  supply  of  carbon  (p.  151).  The  remaining  gases  and 
other  substances  are  impurities  which  usually  occur  in  larger 
amounts  in  the  air  of  towns. 

The  General  Properties  of  Gases.— (i)  Gases  respond 
much  more  readily  to  alterations  of  temperature  than  liquids 
or  solids,  though  these  as  a  rule  increase  in  volume  when 
heated,  and  contract  when  cooled.  The  volume  of  each  liquid 
or  solid  is  altered  to  a  different  extent  by  like  changes  in 
temperature,  but  all  gases  are  affected  equally.  The  nature 
of  the  gas  has  little  or  no  effect,  provided  it  is  one  which  is 
not  easily  liquefied. 

If  a  small  flask  be  fitted  with  a  perforated  rubber  stopper 
and  a  long  bent  glass  tube  in  which  a  short  length  of  mercury 
prevents  escape  of  air  and  acts  as  an  index  of  the  volume  of 
the  air,  very  slight  warming — such  as  that  produced  by  grasping 
the  flask  in  the  hand — will  cause  the  mercury  to  run  along  the 
tube  owing  to  the  increase  in  volume  of  the  gas.  The  actual 
relation  between  the  volume  of  a  gas  and  its  temperature, 
which  is,  as  before  stated,  the  same  for  all  gases,  is  expressed 


AIR 


1 1 


in  the  following  formula,  generally  known  as  Charles's  Law 
(it  was  discovered  by  Charles  of  Paris  in  1787)  :  — 

Every  gas  expands  or  contracts  ^  of  its  volume  at  o°  C.for 
every  increase  or  decrease  of  i°C.,  provided  the pres stir e  remains 
unaltered. 

If  the  volume  is  kept  constant  the  law  will  take  the  form  : 
The  pressure  exerted  by  a  gas  increases  or  decreases  ^  of 
its  pressure  at  o°C.  for  every  increase  or  decrease  of  i°C. 

It  is  obvious  that  if  this  law  held  throughout  all  tempera- 
tures the  gas  would  cease  to  exist  at  —  273°C.,  or,  what  comes 
to  the  same  thing,  it  would  exert  no  pressure.  This  of  course 
would  not  take  place  as  the  gas  would  change  its  state  before 
that  extremely  low  temperature  was  reached  (it  has  not  been 
reached,  up  to  the  present).  This  temperature  "  —273°  C." 
is  often  used  as  a  starting  point  for  the  measurement  of 
temperature.  It  is  referred  to  as  the  absolute  zero  of 
temperature,  and  temperature  reckoned  from  this  point  is 
known  as  absolute  temperature.  We  find  this  particularly 
convenient  when  dealing  with  gaseous  volumes,  for  Charles's 
Law  can  obviously  be  expressed  in  the  form  : — "  The  volume 
of  a  gas  is  proportional  to  its  absolute  temperature."  The 
absolute  temperature  is  found  by  adding  273°  C.  to  the 
temperature  as  shown  by  an  ordinary  Centigrade  thermometer 

(P.  13)- 

(2)  An  even  more  simple  "  law  "  states  the  effect  of  altera- 
tions of  pressure  upon  the  volume  of  a  gas.     It  is  known  as 
Boyle's  Law,  or  Marriotte's  Law,  and  is  generally  expressed 
thus :    The  volume  of  a  gas  is  inversely  as  the  pressure,  when 
the  temperature  remains  unchanged.     This   means  that  if  the 
pressure   on  a  gas  be  doubled,   the  volume  is  halved;   if 
the  pressure  be  trebled,  the  volume  is  reduced  to  one-third, 
and  generally  in  whatever  proportion  the  pressure  is  increased 
the  volume  is  diminished  in  the  same  proportion. 

(3)  Gases  allow  heat  to  pass  through  them  without  being 
perceptibly  warmed ;    they  are  sometimes  said   to  be  trans- 
parent to  heat ;  the  scientific  term  is  "  diathermanous  " 

heat ;  8m,  through). 


12     A   FOUNDATION   COURSE  IN  CHEMISTRY 


(4)  Gases  can  be  liquefied  by  pressure  —  aided,  if  necessary, 
by  reduction  in  temperature  —  or  sometimes  by  reduction  in 
temperature  alone. 

Measurement  of  Atmospheric  Pressure.  —  Air  exerts  pres- 
sure upon  everything  with  which  it  is  in  contact.  This 
pressure  is  generally  measured  by  means  of  some  form  of 
barometer1  (pressure  measurer).  This,  in  its  simplest  form, 
is  merely  a  glass  tube  about  a  yard  in  length.  When  it  is  filled 
with  mercury  and  then  inverted  in  a  reservoir  of  the  same  metal, 
the  mercury  does  not  entirely  flow  out  of  the  vertical 
tube;  a  column  about  30  inches,  or  760  mm.,  high 
remains.  The  height  of  this  column  measures  the 
pressure  of  the  atmosphere.  In  the  case  of  a  tube 
of  i  square  inch  section,  the  mercury  when  stand- 
ing at  a  height  of  30  inches  would  have  a  volume 
of  30  cubic  inches.  Thirty  cubic  inches  of  mercury 
weigh  14!  pounds  Avoirdupois,  and  this  is  the 
amount  of  the  pressure  of  the  atmosphere  upon 
every  square  inch  of  surface  with  which  it  is  in 
contact. 

Thirty  inches,  or  760  mm.,  is  the  average 
height  of  the  barometer  at  sea  level,  and  the 
pressure  supporting  this  height  of  mercury  is  re- 
ferred to  as  a  pressure  of  one  atmosphere.  At 
heights  above  the  sea  level  the  average  pressure 
is  of  course  less,  while  it  is  perceptibly  greater 
in  depths  such  as  mines. 

(Note  that  pressure  is  measured  in  units  of 
length;    i.e.   the   length   of  the   mercury   column 
which  the  pressure  would  support.) 
Measurement  of  Temperature.—  Temperature  is  usually 
measured  by  means  of  a  thermometer.2     This  consists  of  a 
thin  glass  tube,  with  a  bulb  at  one  end,  containing  mercury, 
which  expands  regularly  for  equal  increments  of  temperature. 
Three  forms  of  mercury  thermometer  are  in  use  in  Europe,  the 

1  Gk.  fidpos,  heavy.     Cp.  Baryta,  Barium. 

2  Gk.  6epfji6s,  heat  ;  fifrpov,  a  measure.   A  thermometer,  however,  does 
not  measure  quantities  of  heat,  but  differences  of  temperature. 


FIG.  2. 


AIR 


80° 


180° 


100' 


Boiling 
Point. 


Freezing 
Point 


FIG.  3. 


Fahrenheit,  Centigrade  or  Celsius,  and  the  Re'aumur,  but  they 
differ  only  in  the  graduation  of  the  scale.     On  all  three  the 
same  two  fixed  points  are  taken, 
viz.   the  position  of  the  mercury 
when  the  thermometer  is  placed 
in  melting   ice,  and   its   position 
when    in   the    steam    of    boiling 
water.     The  first  is  known  as  the 
freezing  point,  the  second  as  the 
boiling  point  of  water.    The  differ- 
ence between  the  graduations  of 
the  three  thermometers  is  shown 
in  Fig.  3.1 

Corrections  of  Gaseous  Volume 
for  Temperature  and  Pressure. — 
Gaseous  volumes  are  always  com- 
pared with  one  another  at  a 

pressure  of  760  mm.  and  at  a  temperature  of  o°  C.  These 
are  known  as  normal  temperature  and  pressure,2  but  as  gases 
can  seldom  or  ever  be  measured  under  exactly  these  condi- 
tions, calculations  for  finding  the  volume  of  the  gas  at  N.T.P. 
have  to  be  undertaken.  An  example  is  here  given  :  150  c.c. 
of  dry  gas  are  measured  at  15°  C.  and  740  mm.  pressure ; 
what  volume  will  the  gas  occupy  at  N.T.P.  ? 

(a)  The  volume  of  the  gas  is  proportionate  to  the  absolute 

temperature  and  15°  C.  is  15  +  273  =  288°  C.  abso- 
lute, and  o°  C.  is  273°  C.  ab.  It  will  measure  less 
at  273°  than  at  288°;  we  therefore  multiply  by  273 
and  divide  by  288. 

150  *  273  c.c.  (corrected  for  temperature). 

2oo 

(b)  The  volume  of  the  gas  is  inversely  proportionate  to  the 

1  To  convert  degrees  on  one  thermometer  into  their  equivalent  on 
another  the  following  formulae,  the  explanation  of  which  will  be  obvious, 
can  be  used — 

F.  =|C. +32  F.  =|R. +  32  C.  =JR. 

'  The  abbreviation  N.T.P,  is  often  used  for  these  words, 


14     A   FOUNDATION   COURSE    IN  CHEMISTRY 

pressure.  It  will  therefore  measure  less  at  760  mm. 
than  at  740 ;  we  therefore  multiply  by  740  and  divide 
by  760. 

150  X  273  x  74Q  c.c.  (corrected  for  temperature 

1  x  76o  and  pressure). 

If  the  gas  be  saturated  with  water  vapour,  the  pressure 
exerted  by  the  latter  must  be  subtracted  from  the  total  gaseous 
pressure,  before  the  corrections  are  made. 


CHAPTER    III 

THE    CHIEF    GASES    OF    THE   ATMOSPHERE 

Oxygen.1— Oxygen  is  the  most  plentiful  element  in  nature. 
We  have  seen  that  it  occurs  in  air  to  the  extent  of  21  per 
cent. ;  in  the  next  chapter  we  shall  see  that  it  is  also  one  of 
the  constituents  of  water.  In  addition  to  this,  it  occurs  com- 
bined with  other  elements  in  most  rocks  and  in  the  tissues 
of  plants  and  animals. 

The  gas  was  prepared  in  the  year  1774  by  Priestley,  a 
chemist,  living  in  Birmingham ;  and  at  about  the  same  time 
by  Scheele,  a  Swedish  chemist.  Triey  each  prepared  it  by 
heating  the  substance  then  known  to  chemists  as  "  red  pre- 
cipitate "  or  "  mercurius  caldnatus  per  se  " ;  which  we  have 
already  met  with  as  the  red  powder  formed  on  mercury  when 
it  is  gently  heated  in  air  for  a  long  time.  This  substance,  on 
being  strongly  heated,  decomposes  into  mercury  and  oxygen, 
and  the  gas  may  be  collected  in  suitable  jars,  over  water. 

It  is  a  colourless,  odourless  gas,  very  slightly  soluble  in 
water,  and  neutral  to  litmus.  It  is  a  little  heavier  than  air 
(i  litre  weighs  1*43  grams),  its  density  compared  with 
hydrogen 2  is  16  (p.  34).  Its  general  chemical  properties 
are  such  as  to  make  it,  to  us,  perhaps  the  most  important  of 
all  the  elements. 

1  Gk.  b£vs,  sour  ;  -yewta,  I  produce.     The  name  was  given  to  the  gas 
by  Lavoisier  on  the  incorrect  assumption  that  it  was  the  essential  constituent 
of  acids.     The  name  "  Fire  Air  "  which  was  also  given  to  the  gas  would 
have  been  much  more  descriptive  of  its  properties. 

2  Hydrogen  is  the  lightest  gas  known,  and  is  therefore  taken  as  the 
standard  with  which  other  gases  are  compared  as  regards  density. 


1 6     A   FOUNDATION   COURSE    IN    CHEMISTRY 

If  we  put  a  glowing  splinter  of  wood  into  a  jar  of  oxygen, 
the  splinter  immediately  bursts  into  flame  and  burns  vigorously. 
The  same  increased  energy  of  combustion  is  seen  when  other 
burning  substances  are  placed  in  the  gas.  If,  for  instance,  a 
piece  of  sulphur,  which  burns  in  air  with  a  dark  blue  flame,  be 
put,  after  being  lighted,  into  a  jar  of  oxygen,  the  flame  increases 
considerably  in  size,  becomes  brightly  luminous,  and  of  a 
pale  blue  colour.  Phosphorus  burns  in  oxygen  with  dazzling 
brightness ;  and  charcoal,  which  in  air  only  glows  feebly,  burns 
in  oxygen  with  much  greater  rapidity  and  brilliancy.  Many 
-substances  which  will  not  burn  in  air  will  burn  brightly  in 
oxygen.  Perhaps  the  most  striking  effect  is  obtained  with 
iron.  If  a  piece  of  watch  spring  tipped  with  burning  sulphur 
be  put  into  a  jar  of  oxygen,  the  iron  burns  rapidly,  throwing 
off  brilliant  sparks. 

The  chemical  change  in  all  these  cases  is  "  Combination." 
The  sulphur,  phosphorus,  carbon,  or  iron,  combines  with  the 
oxygen  to  form  a  compound  known  as  an  oxide.  The  oxides 
of  sulphur  and  carbon  are  gaseous,  the  oxide  of  phosphorus  is 
the  white  compound  mentioned  on  page  99,  the  oxide  of  iron 
is  a  brown  solid.  Much  heat  is  given  out  when  these  com- 
binations with  oxygen  take  place,  and  the  burning  substance 
itself,  or  the  products  of  the  reaction,  often  become  white  hot 
or  incandescent.  The  phenomenon  is  called  "  Combustion." 
Ordinary  combustion  consists  in  combination  with  oxygen 
accompanied  by  the  evolution  of  light  and  heat,  and  for  this 
reason  oxygen  is  often  referred  to  as  the  supporter  of  com- 
bustion. The  relation  of  the  air  to  combustion  is  shown  in  the 
experiments  described  on  pages  8  and  9,  particularly  that  on 
page  9,  where  the  oxygen  gas  is  obtained  separately.  It  is 
the  presence  of  oxygen  in  the  air  which  allows  combustion 
to  take  place. 

The  term  "  supporter  of  combustion  "  requires  examination. 
In  the  case  of  a  flame  at  an  ordinary  gas-burner,  we  should 
refer  to  the  coal  gas  as  the  combustible  body,  and  the  air 
around  it  as  the  supporter  of  the  combustion.  But  if  a  lamp 
chimney  be  fitted,  as  shown  in  the  illustration  (Fig.  4),  in 
which  A  is  a  short,  wide,  brass  or  glass  tube,  B  a  smaller  tube 


THE   CHIEF   GASES   OF   THE   ATMOSPHERE    17 

connected  with  the  gas  supply,  and  C  a  piece  of  asbestos  board, 
perforated  with  a  small  hole,  and  the  lamp  be  first  filled  with 
coal  gas,  and  the  hole  in  the  cardboard  closed  until  the  gas 
comes  out  from  the  tube  A.  If  then  a  light  be  applied  to  the 
issuing  gas,  on  opening  the  hole  in  the  cardboard,  the  flame 
will  be  drawn  up  the  tube  A  and  will  be  seen,  inside  the  lamp 
chimney,  surrounded  by  the  coal  gas.  In  this  case  we  should 
be  justified  in  saying  that  the  oxygen  of  the  air  was  the 
combustible  body,  and  the  coal  gas  the  supporter  of  com- 
bustion. In  truth,  the  term  is  applicable  to  either,  but  it  is 
generally  applied  to  that  gas  which  surrounds  the  flame,  and 
in  all  ordinary  circumstances  this  is  air, 
or  oxygen.1  If  we  lived  in  an  atmosphere 
of  coal  gas  we  might  be  burning  oxygen 
at  gas-jets. 

The  rusting  of  iron  is  an  example  of 
very  slow  combination  with  oxygen.  If 
some  clean  iron  filings,  moistened  with 
water,  be  suspended  in  a  muslin  bag,  in 
a  jar  of  air  standing  over  water,  and 
allowed  to  remain  for  several  days,  the 
iron  becomes  very  "  rusty,"  and  the  water 
rises  just  as  if  phosphorus  had  been  burnt 
in  the  jar,  and  to  the  same  height.  Iron, 
therefore,  when  moistened,  removes  oxygen  from  the  air, 
forming  iron  rust,  which  is  oxide  of  iron  combined  with 
water. 

The  amount  of  heat  given  out  on  combination  with  oxygen 
is  different  for  each  substance,  but  for  any  given  kind  of 
material  it  is  proportional  to  the  mass  of  the  substance  which 
enters  into  combination.  Thus,  when  i  gram  of  carbon  is 
burned  completely  96,960  units2  of  heat  are  evolved.  One 

1  We  have  referred  to  oxygen  as  "  the  supporter  "  not  "  a  supporter  " 
of  combustion.      As  ordinary  combustion  consists  in  combination  with 
oxygen,  oxygen  is  the  only  possible  supporter  of  combustion  of  this  type. 
Other  kinds   of  combustion   will   be   referred   to   when   treating  of  the 
chemistry  of  other  elements. 

2  A  unit  of  heat  is  the  amount  of  heat  required  to  raise  I  gram  of 
water  through  1°  C. 

C 


FIG.  4. 


i8     A  FOUNDATION   COURSE   IN  CHEMISTRY 

gram  of  hydrogen  on  burning  causes  the  evolution  of  68,360 
units  of  heat.  If  combination  takes  place  rapidly,  the  heat  is 
given  out  rapidly,  and  the  substances  get  very  hot ;  but  if  the 
combination  takes  place  slowly,  the  heat  is  evolved  slowly,  and 
the  temperature  is  not  appreciably  raised.  Although  the  two 
actions  are  absolutely  identical,  the  difference  between  the 
temperature  produced  by  iron  rapidly  burning  in  oxygen  and 
slowly  rusting  in  air  is  an  instance  of  the  effect  of  increasing 
the  rapidity  of  the  chemical  action.  A  more  familiar  example 
is  seen  in  the  effect  of  forcing  air  through  a  fire  by  means  of 
bellows,  and  so  giving  the  fire  a  continual  supply  of  fresh 
oxygen.  The  fire  burns  more  rapidly  and  becomes  much 
hotter,  as  the  heat  given  out  by  the  burning  coal  is  evolved  in 
a  shorter  time.  In  general,  the  faster  anything  burns  the 
higher  the  temperature  produced.  Nearly  all  elements  combine 
with  oxygen ;  although  several  will  not  do  so  directly,  they  can 
be  made  to  combine  by  various  indirect  methods. 

When  substances  combine  with  oxygen  slowly  (e.g.  the 
rusting  of  iron)  they  are  sometimes  said  to  undergo  slow 
combustion.  Heat  is  given  out,  but  not  with  sufficient  rapidity 
to  cause  incandescence  or  flame.  The  respiration  of  animals 
may  be  looked  upon  as  an  instance  of  slow  combustion,  and 
this  statement  shows  why  oxygen  is  necessary  for  the  support 
of  animal  life.  The  effect  upon  animals  of  removing  the 
oxygen  from  the  air  is  to  cause  suffocation  and  death,  while 
increase  in  the  percentage  of  oxygen  leads  to  increased  activity 
within  certain  limits.  Animals,  however,  could  not  long  con- 
tinue to  breathe  pure  oxygen ;  it  would  act  as  a  poison,  pro- 
ducing intense  inflammation,  convulsions,  and  death. 

Although  oxygen  occurs  free  in  the  atmosphere,  its  separa- 
tion in  a  pure  state  presents  considerable  difficulties.  It  is 
therefore  generally  prepared  in  the  laboratory  from  certain  of 
its  compounds.  Some  of  the  oxides  are  suitable  for  the 
purpose.  Manganese  dioxide  is  sometimes  used.  This 
substance,  when  strongly  heated,  loses  a  portion  of  its  oxygen. 
Red-lead  (p.  209)  and  oxide  of  mercury  (p.  210)  have  already 
been  shown  to  behave  in  a  similar  manner,  but  none  of  these 
provide  a  perfectly  satisfactory  method  of  preparation,  for 


THE   CHIEF  GASES  OF  THE  ATMOSPHERE    19 

the  amount  of  oxygen  evolved  is  small  in  comparison  with  the 
weight  of  oxide  used,  and  in  the  case  of  mercury  oxide  the 
substance  itself  is  somewhat  expensive. 

The  material  most  generally  employed  is  potassium 
chlorate,  a  compound  of  oxygen  with  the  elements  chlorine 
and  potassium.  This  compound,  on  being  heated  strongly, 
loses  all  its  oxygen,  and  leaves  a  residue  consisting  of  potassium 
combined  with  chlorine  only.  Admixture  with  certain  other 
substances  causes  potassium  chlorate  to  part  with  its  oxygen 
at  a  lower  temperature ;  manganese  dioxide  is  most  often  used, 
but  a  still  more  powerful  effect  is  produced  by  iron  oxide, 
and  even  powdered  glass  or  sand  facilitate  the  liberation  of 
the  gas.  In  all  cases  only  the  potassium  chlorate  undergoes 
decomposition. 

The  apparatus  employed  for  the  preparation  of  small 
quantities  of  oxygen  is  shown  in  the  illustration  (Fig.  5). 

Oxygen  is  an  article  of  com- 
merce and  is  used  largely  both 
for  medical  purposes  and  in 
various  industries.  It  is  sup- 
plied under  great  pressure  in 
wrought-iron  cylinders. 

The  usual  commercial 
method  for  preparing  oxygen 
is  a  process  of  obtaining  it 
indirectly  from  the  air. 

When  barium  oxide,  a  sub- 
stance very  like  quick-lime,  is 

heated  in  air  or  oxygen  to  a  temperature  not  exceeding  55o°C. 
it  combines  with  additional  oxygen  forming  barium  peroxide. 
This  is  decomposed  again  into  barium  oxide  and  oxygen 
when  more  strongly  heated.  By  alternately  heating  and  cool- 
ing barium  peroxide  a  continual  supply  of  oxygen  may  be 
obtained,  without  any  decrease  in  the  amount  of  barium 
oxide.  This  is  obviously  an  economical  method,  but  as  it  is 
inconvenient  and  expensive  to  continually  raise  and  lower  the 
temperature,  the  barium  compound  is  kept  at  a  constant  high 
temperature  and  the  pressure  varied  by  means  of  air  pumps. 


FIG.  5. 


20     A  FOUNDATION   COURSE    IN   CHEMISTRY 

When  the  pressure  is  high  the  substance  takes  up  oxygen 
from  the  air,  and  when  the  pressure  is  reduced  the  oxygen  is 
again  evolved  and  may  be  collected. 

Another  method  of  obtaining  oxygen  from  the  air  promises 
to  become  of  commercial  importance.  Air  liquefied  by  intense 
cold  and  great  pressure  is  allowed  to  evaporate  freely  at 
ordinary  atmospheric  pressure.  Under  these  conditions  the 
nitrogen  boils  away  first,  leaving  a  liquid  which  may  contain 
as  much  as  95  per  cent,  of  oxygen.  The  temperature  at 
which  this  evaporation  takes  place  is  of  course  very  low,  for 
nitrogen  boils  at  — 194°  C.,  while  the  boiling  point  of  oxygen 
is  —182*5°  C.  The  gas  obtained  by  evaporation  of  the 
residual  liquid  is  pumped  into  cylinders  and  sold  as  compressed 
oxygen. 

Liquid  oxygen  is  pale  blue  in  colour.  Gaseous  oxygen  is 
soluble  in  water  to  the  extent  of  about  4  volumes  of  the  gas  in 
100  of  water  at  o°  C.  Fish  derive  the  oxygen  they  need  from 
this  source,  their  gills  being  the  respiratory  organs  by  which 
they  make  use  of  the  dissolved  gas.1 

By  passing  an  electric  spark  through  oxygen,  or  by  sub- 
mitting it  to  the  silent  electric  discharge,  oxygen  is  caused  to 
undergo  contraction  in  volume,  and  a  modified  form  of  the 
gas  is  produced  which  is  known  as  ozone  (p.  92). 

1  Despite  the  fact  that  respiration  and  combustion  are  both  processes  of 
oxidation,  they  stand  in  a  somewhat  different  relation  to  the  amount  of  oxygen 
in  the  air.  In  the  case  of  the  former,  it  is  the  actual  quantity  of  oxygen 
that  is  important ;  in  the  latter  it  is  the  percentage.  When  the  amount  of 
oxygen  in  air  is  reduced,  animals  unconsciously  breathe  more  deeply 
and  so  take  in  more  oxygen.  Human  beings  experience  no  inconvenience 
even  when  one-third  of  the  oxygen  normally  present  in  the  air  is  removed, 
i.e.  when  it  is  reduced  to  14  per  cent.  But  if  the  amount  of  oxygen  be 
reduced  to  10  per  cent,  (less  than  half),  the  air, will  not  properly  support 
respiration  and  persons  breathing  it  experience  some  of  the  sensations 
of  suffocation. 

Burning  substances  differ  widely  from  one  another  in  their  sensitiveness 
to  deficiency  of  oxygen  ;  thus  the  flame  of  marsh  gas  (p.  139)  is  extinguished 
when  the  amount  of  oxygen  in  the  air  is  reduced  to  17^  per  cent.,  and  that 
of  a  candle  when  the  oxygen  is  reduced  to  1 7  per  cent.  Hydrogen  continues 
to  burn  till  only  7j  percent,  of  oxygen  is  left,  and  phosphorus,  till  practically 
all  the  oxygen  is  removed.  It  will  be  seen,  therefore,  that  the  popular 
notion  that  air  which  extinguishes  a  candle  flame  is  not  capable  of  sup- 
porting respiration  is  not  based  on  fact  j  such  air  may  or  may  not  be  fit  to 
breathe. 


THE   CHIEF   GASES   OF   THE   ATMOSPHERE    21 

Nitrogen. — The  facts  we  have  already  discovered  in  con- 
nection with  the  gas  are :  it  is  colourless,  tasteless,  odourless, 
neutral  to  litmus,  less  soluble  in  water  than  oxygen,  and 
chemically  very  inactive.  In  fact  it  exhibits  less  tendency  to 
unite  with  other  elements  than  any  other  of  the  common  gases. 
Its  most  important  properties  are  therefore  of  a  negative 
character.  It  is  obviously  not  poisonous,  and  in  the  air  its 
chief  function  is  to  dilute  the  oxygen.  A  few  substances,  such 
as  magnesium  and  potassium,  combine  with  nitrogen  when 
heated  strongly,  and  at  the  temperature  of  the  electric  spark 
the  gas  combines  with  oxygen,  a  fact  of  great  importance  in 
agriculture  (p.  132).  A  certain  amount  of  combination  of  these 
gases  takes  place  during  thunderstorms. 

It  has  already  been  shown  that  nitrogen  can  be  obtained 
from  the  air  by  burning  phosphorus  (p.  8)  in  it.  A  better 
method  is  to  pass  the  air  over  heated  copper ;  this  forms  copper 
oxide  and  leaves  the  nitrogen,  which  can  be  collected  over 
water.  Burning  a  candle  in  air  would  not  be  effective,  for  not 
only  would  the  nitrogen  left  be  mixed  with  the  products  of 
combustion  (carbon  dioxide  and  water  vapour)  but  the  candle 
would  be  extinguished  long  before  all  the  oxygen  was  removed 
from  the  air. 

These  can  scarcely  be  regarded  as  methods  of  preparing 
nitrogen ;  they  are,  rather,  ways  of  removing  the  oxygen  with 
which  it  is  mixed,  and,  moreover,  the  nitrogen  thus  obtained 
still  contains  other  inactive  gases,  the  presence  of  which  causes 
it  to  be  slightly  heavier  than  the  pure  gas. 

Nitrogen  is  most  easily  prepared  in  a  pure  state  from 
ammonium  nitrite,  which,  on  heating,  decomposes  entirely 
into  nitrogen  and  water.  It  is  convenient  to  use  a  mixture 
of  sodium  nitrite  and  ammonium  chloride  dissolved  in  water. 
The  gas  is  collected  over  water. 

Nitrogen  is  an  essential  constituent  of  the  tissues  (fats  and 
certain  others  excepted)  which  form  the  bodies  of  plants  and 
animals,  and  is  necessary  for  their  growth.  No  animals,  and 
very  few  plants,  however,  can  utilise  free  nitrogen.  Plants  in 
general  require  that  it  should  be  supplied  in  the  form  of  com- 
paratively simple  compounds;  animals  obtain  their  nitrogen 


22     A  FOUNDATION   COURSE    IN  CHEMISTRY 

from  foods,  e.g.  flesh,  casein,  gluten,  etc.,1  which  are  compounds 
of  a  much  more  complex  nature. 

Some  plants,  such  as  the  leguminosae,  apparently  take  up 
atmospheric  nitrogen.  This  is  effected  by  means  of  certain 
bacteria  which,  being  present  in  the  soil,  enter  the  root  hairs 
and  grow  inside  the  cortex  producing  small  tubercles.  These 
bacteria  assimilate  nitrogen  directly  from  the  air  and  convert 
it  into  compounds  which  the  plant  is  able  to  utilise. 

1  Some  plants,  Dionaea  (Venus'  fly-trap),  Drosera  (sun  dew),  the 
various  forms  of  pitcher  plant  (Nepenthes),  have  the  power  of  assimilating 
nitrogen  from  highly  complex  compounds  such  as  those  which  form  the 
bodies  of  insects. 


CHAPTER   IV 

WATER 

No  substance  is  more  familiar  than  water.  It  exists  in  such 
immense  quantities  that  it  covers  by  far  the  greater  part  of  the 
earth's  surface.  Although  it  is  so  common,  it  is  difficult  to 
obtain  in  a  perfectly  pure  condition,  owing  to  the  fact  that  it 
dissolves,  to  a  greater  or  less  extent,  such  a  large  number  of 
substances,  solid,  liquid,  or  gaseous.  Natural  waters  invariably 


CoU  Wttfr  Supply 


Water  Exit 

FIG.  6. 


contain  such  substances  in  solution.  Water  also  often  contains 
solid  particles  which  have  not  dissolved,  but  remain  suspended 
in  the  liquid.  They  can  be  separated  by  nitration.  The  filter 
used  in  laboratories  is  generally  a  circular  piece  of  purified 
paper,  folded  in  four,  opened  so  as  to  form  a  cone  and  fitted 


24     A   FOUNDATION    COURSE   IN  CHEMISTRY 

into  a  funnel.  Substances  in  solution  cannot  be  removed 
by  nitration ;  in  order  to  effect  this  the  liquid  must  be 
distilled 

A  form  of  apparatus  in  common  use  is  shown  in  the 
diagram  (Fig.  6).  A  is  a  flask  containing  the  water  to  be 
distilled ;  it  has  a  side  tube  in  the  neck,  and  is  fitted  with  a 
cork  through  which  a  thermometer  is  passed.  The  water  in  A 
is  boiled,  and  the  steam  passes  by  the  side  tube  through  the 
condenser  B.  This  consists  of  a  straight  tube  surrounded  by  a 
jacket  of  cold  water  which  enters  at  C  and  leaves  the  con- 
denser at  D.  The  condensed  steam  is  collected  in  the  flask 
E.  The  distilled  water  thus  obtained  is  free  from  solids  in 
solution,  and  if  the  first  portion  of  the  distillate  is  rejected,  it 
is  also  free  from  dissolved  gases. 

The  temperature  at  which  water  boils  at  ordinary  pressure 
is,  as  has  already  been  shown,  one  of  the  fixed  points  on  the 
thermometer,  and  is  marked  on  the  Centigrade  scale  as  100°. 
The  boiling  point  is,  however,  dependent  upon  the  atmospheric 
pressure.  The  higher  the  pressure,  the  higher  the  temperature 
to  which  the  water  must  be  raised  before  it  boils.  If  the  pres- 
sure be  low  enough  water  can  be  made  to  boil  when  it  is  almost 
cold.  The  apparatus  described  on  page  8  (Fig.  i)  may  be 
used  to  illustrate  this. 

Boil  the  water  and  close  the  indiarubber  tube,  as  described, 
and  then  hold  the  flask  under  the  tap  and  pour  cold  water 
upon  it.  The  water  which  ceased  boiling  when  the  flame 
was  removed,  will  again  begin  to  boil,  and  can,  by  continuous 
cooling,  be  made  to  do  so  until  the  flask  scarcely  seems  warm 
to  the  hand.  For  this  experiment  to  be  successful,  it  is  essential 
that  all  the  air  should  have  been  driven  out  of  the  flask,  for 
the  water  boils  at  the  lower  temperature  because  the  rapid 
cooling  condenses  the  steam  and  thereby  lowers  the  pressure 
inside  the  flask. 

Pure  water  is,  at  ordinary  temperatures,  a  tasteless,  odour- 
less liquid,  colourless  when  viewed  in  small  quantity,  but  pale 
greenish  blue  when  seen  in  considerable  thickness.  It  has  no 
effect  upon  the  colour  of  litmus ;  that  is,  it  is  neither  acid  nor 
alkaline  (pp.  53,  54). 


WATER  25 

Physical  Properties  of  Water. — It  is  a  very  feeble  con- 
ductor of  heat.  This  can  be  demonstrated  by  heating  a  test- 
tube  full  of  water  near  the  top  ;  the  water  in  the  upper  portion 
will  boil,  while  that  at  the  bottom  remains  quite  cold.  In  order, 
therefore,  to  raise  the  temperature  of  large  quantities  of  water, 
it  is  necessary  to  apply  heat  from  below.  Like  most  other  sub- 
stances, water  expands  when  heated  and  so  becomes  less  dense. 
When,  therefore,  a  vessel  of  water  is  placed  over  a  flame,  the 
water  nearest  the  flame  gets  heated  first,  and  becoming  less 
dense,  rises  through  the  cooler  and  heavier  liquid  which  streams 
down  to  take  its  place.  A  system  of  currents,  known  as  con- 
vection currents,  is  thus  set  up  which  gradually  distributes  the 
heated  water  through  the  whole  mass,  until  it  has  all  been 
heated  to  the  boiling  point. 

This  method  of  heating  does  not  apply  to  water  only,  but 
to  most  liquids  and  gases ;  air,  for  example,  is  warmed  by  con- 
tact with  the  heated  surface  of  the  ground,  and  it  is  partly 
by  this  means  that  the  air  currents  known  as  winds  are 
produced. 

If  instead  of  heating  the  water  we  cool  it,  it  will  contract 
in  volume  and  become  denser  until  the  temperature  of  4°  C. 
(39*4°  Fahr.)  is  reached,  when,  unlike  other  liquids,  it  will  on 
further  cooling  begin  to  expand,  and  the  expansion  will  con- 
tinue until  the  freezing  point  is  reached.  At  the  moment  of 
the  change  in  state  there  is  a  great  increase  in  volume,  so  that 
ice  is  considerably  lighter  than  water,  and  floats  upon  it ;  its 
density  as  compared  with  water  is  0*91.  The  expansion  of 
water  on  being  cooled  below  4°  C.  explains  why  ice  is  formed 
on  the  surface  of  lakes  and  not  at  the  bottom,  while  the  expan- 
sion on  freezing  is  the  cause  of  the  ice  being  pushed  up  the 
banks ;  it  accounts  also  for  the  bursting  of  water-pipes  during 
hard  frost.  Of  course,  the  breaking  of  the  pipe  is  not  generally 
noticed  until  the  thaw  comes  when  the  water  from  the  melting 
ice  escapes.  Rocks  are  also  split  by  the  freezing  of  water  in 
their  crevices,  and  soils  are  pulverized. 

The  presence  of  substances  in  solution  lowers  the  freezing 
point  and  raises  the  boiling  point  of  water  (p.  116). 

When  heat  is  applied  to  ice  it  melts.     If  a  thermometer  is 


26     A   FOUNDATION    COURSE    IN   CHEMISTRY 

placed  in  melting  ice  and  the  mass  is  kept  stirred,  the  thermo- 
meter will  indicate  no  rise  in  temperature  as  long  as  any  ice 
remains  unmelted.  The  heat  has  been  used  entirely  in  causing 
change  of  state.  The  amount  of  heat  necessary  to  melt  a  sub- 
stance is  usually  referred  to  as  the  latent  heat  of  the  liquid. 
Thus,  in  the  case  of  ice,  the  heat  necessary  to  turn  it  into  water 
is  called  the  latent  heat  of  water.  Similarly,  the  heat  required 
to  change  water  into  steam  is  called  the  latent  heat  of  steam. 
The  quantities  of  heat  requisite  to  bring  about  these  changes 
of  state  are  large ;  the  heat  used  in  melting  i  gram  of  ice  is 
sufficient  to  raise  the  temperature  of  80  grams  of  water  through 
i°  C.,  i.e.  80  units  of  heat,1  while  as  much  as  537  units  of  heat 
are  required  to  vaporise  i  gram  of  water. 

When  water  is  heated,  its  temperature  rises  very  slowly. 
If,  for  example,  equal  masses  of  mercury  and  water  were 
separately  caused  to  receive  heat  at  equal  rates,  the  mercury 
would  get  hot  much  more  rapidly  than  the  water,  and  the 
same  statement  applies  in  varying  degrees  to  all  other  sub- 
stances. In  other  words,  water  takes  more  heat  to  make  it  hot 
than  does  any  other  substance.  It  is  said  to  have  a  larger  capa- 
city for  heat  (thermal  capacity)  or  to  have  a  high  specific  heat.'2 
This  property  of  water  is  of  great  importance,  for  substances 
which  when  heated  get  hot  slowly  also  cool  slowly.  It  is  for 
this  reason  that  hot  water  and  steam  are  used  for  warming 
houses ;  and  absence  of  extremes  of  summer  heat  and  winter 
cold  in  insular  climates  is  due  to  the  moderating  effect  of  the 
water  of  the  ocean. 

Solutions. — Water  is  a  very  general  solvent.  It  dissolves 
most  substances  to  an  appreciable  extent,  but  the  permanent 
tissues  of  plants  and  animals,  indiarubber,  resins,  and  some 

1  P.  17,  note  (2). 

2  These  two  terms  do  not  mean  exactly  the  same  thing.     The  thermal 
capacity  of  a  substance  is  the  number  of  units  of  heat  required  to  raise 
I   gram   of    the   substance    through    i°  Centigrade,    and   is   therefore  a 
quantity  of  heat.     The  specific  heat  is  the  ratio — 

Heat  required  to  raise  a  given  mass  of  the  substance  through  i°  C. 
Heat  required  to  raise  the  same  mass  of  a  standard  substance  through  1°  C. 

and  water  is  always  taken  as  the  standard  substance. 


WATER 


others  are  practically  insoluble.  Soluble  substances,  moreover, 
differ  greatly  in  their  degree  of  solubility,  and  for  each  substance 
the  amount  that  will  dissolve  depends  upon  the  temperature 


f50   _ 


SI 


-Sodium 


/I 


Chloride^ 


O    5   1O  15  2O        3O       4O      5O        6O       7O       8O      90 

Temperature  in  Decrees  Centigrade. 

FIG.  7.— SOLUBILITY  CURVES. 


fOO 


28     A  FOUNDATION   COURSE    IN  CHEMISTRY 

of  the  water.  Generally,  a  rise  of  temperature  causes  the  water 
to  dissolve  a  larger  quantity  of  the  solid.  In  some  cases  this 
is  very  marked.  Chloride  of  lead  dissolves  in  hot  water  with 
comparative  ease,  while  its  solubility  in  cold  water  is  very 
small.  On  the  other  hand,  common  salt  is  nearly  as  soluble  in 
cold  water  as  in  hot.  It  is  customary  to  represent  graphically, 
in  the  form  known  as  a  "  Solubility  Curve,"  the  relation  between 
temperature  and  the  quantity  which  enters  into  solution. 
Fig.  7  is  a  series  of  curves  for  certain  well-known  substances. 
The  temperature  is  marked  on  the  bottom  horizontal  line,  the 
vertical  measurements  give  the  number  of  grams  of  the  sub- 
stance in  100  c.c.  of  the  saturated  solution. 

Liquids  which  are  soluble  in  water  are  generally  said  to  be 
miscible  with  water.  Alcohol  is  miscible  with  water  in  all  pro- 
portions, and  so  is  sulphuric  acid ;  but  other  liquids,  such  as 
ether,  chloroform,  and  oils,  are  either  insoluble  or  only  dissolve 
to  a  slight  extent.  When  shaken  with  water  and  allowed  to 
stand  they  separate,  the  lighter  liquid  forming  the  upper  layer. 
In  the  case  of  ether  this  upper  layer  would  be  ether  mixed  with 
a  little  water,  while  the  lower  layer  would  be  water  mixed  with 
a  small  quantity  of  ether. 

The  solubility  of  gases  in  water  depends  not  only  upon 
temperature  but  also  upon  pressure.  As  a  general  rule,  increase 
of  temperature  rapidly  diminishes  the  solubility  of  gases  in 
water,  so  that  it  is  often  possible  to  expel  all  the  gas  from  solu- 
tion by  boiling,  hydrochloric  acid  (p.  78)  is  an  important 
exception.  Increase  of  pressure  increases  the  solubility  of 
gases.  Carbon  dioxide,  for  example,  is  not  very  soluble  in 
water,  but  in  the  manufacture  of  aerated  waters  it  is  forced  into 
water  under  great  pressure  and  remains  dissolved.  When  the 
cork  is  removed  from  the  bottle  the  gas  escapes  with  brisk 
effervescence  because  the  pressure  is  reduced. 

Crystallisation. — When  water  at  any  temperature  has  dis- 
solved as  much  of  a  solid  as  it  is  capable  of  doing,  the  solution 
is  said  to  be  saturated.  If  the  temperature  of  the  saturated 
solution  be  raised  it  is  generally  no  longer  saturated,  but  will 
take  up  a  further  quantity  of  the  solid.  If  the  temperature  of 
the  saturated  solution  be  lowered  part  of  the  solid  will  separate 


WATER  29 

until  only  sufficient  remains  dissolved  to  saturate  the  solution 
at  the  lower  temperature.  The  solid  generally  separates  in  the 
crystalline  form.  The  crystals  of  each  kind  of  substance 
have  a  characteristic  shape.  They  have  flat  surfaces1  and 
straight  edges,  but  they  are  of  many  different  forms.  Crystals 
may  also  be  formed  by  allowing  the  solution  to  evaporate.  If 
a  solution  is  saturated  when  a  certain  quantity  of  water  is 
present,  some  of  the  solid  must  separate  when  part  of  the  water 
is  removed.  The  more  slowly  evaporation  takes  place  the 
larger  are  the  crystals  formed. 

In  many  cases  crystals  which  are  apparently  quite  dry  con- 
tain water.  Such  water  is  known  as  water  of  crystallisation.2 
When  this  water  is  removed,  the  substance  loses  its  crystalline 
form.  Occasionally  crystals  lose  water  on  exposure  to  the  air 
and  become  covered  with  a  powder ;  they  are  said  to  "  effloresce." 
Some  substances  take  water  from  moist  air  and  dissolve  in  it ; 
they  are  said  to  be  deliquescent. 

In  many  cases  the  presence  of  water  of  crystallisation  alters 
the  colour  of  a  substance.  Thus,  copper  sulphate,  which,  when 
anhydrous  (i.e.  without  water)  is  yellowish  white,  forms  blue 
hydrated  crystals ;  and  the  salts  of  cobalt  are  generally  pink 
when  they  contain  water,  but  are  blue  when  anhydrous. 

Natural  Waters. — Natural  waters  always  contain  many 
impurities  in  solution.  Rain-water — particularly  that  which  falls 
in  country  districts  after  a  previous  rainy  period — is  the  purest, 
but  even  this  contains  foreign  matter  washed  out  of  the  atmo- 
sphere. Sea-water  has  common  salt  and  other  substances  dis- 
solved in  it.  Water  from  rivers,  lakes,  and  springs  contains 
impurities,  generally  harmless.  The  nature  of  these  depends 
upon  the  nature  of  the  rocks  with  which  the  water  has  been  in 
contact.  The  waters  of  some  springs  contain  considerable 
quantities  of  mineral  matter  in  solution,^-,  salts  of  iron,  calcium, 
magnesium,  potassium,  and  sodium,  and  compounds  of  sulphur. 
Such  springs  are  often  known  as  mineral  springs.  In  some 
cases  the  water  is  so  highly  charged  with  carbon  dioxide  as  to 

1  There  are  substances  which  occasionally  occur  as  crystals  with  curved 
faces.     The  diamond  is  the  most  important  example. 

2  Water  of  hyd  ration  is  perhaps  a  better  term. 


30     A  FOUNDATION   COURSE   IN  CHEMISTRY 

be  strongly  effervescent.  Water  containing  large  quantities  of 
the  salts  of  calcium  or  magnesium  is  said  to  be  hard  (p.  69). 
Water  used  for  domestic  purposes  should  be  examined,  not 
only  to  ascertain  the  degree  of  "  hardness,"  but  also  with  special 
reference  to  the  organic  matter  it  may  hold  in  solution.  This 
organic  matter  is  often  present  owing  to  admixture  with  sewage. 
The  organic  matter  itself  may  be  harmless,  but  the  bacteria  of 
putrefaction  and  disease  which  may  come  with  it  are  extremely 
dangerous. 

ANALYSES  OF  TYPICAL  NATURAL  WATERS 
PARTS  PER  100,000 


Hardness. 

Nitro  • 

Free  am- 
monia. 

Albu; 

minuid 
ammonia. 

Chlorine. 

Total 
solids. 

gen  as 
nitrates 
and 
nitrites. 

Tempo- 
rary. 

Per- 
manent. 

Rain  water  .     . 

0-024 

0-OI5 

0'22 

2,5    !     - 

O'OO3 

Upland  surface 

water  .     .     . 
Deep  well  water 

0-O02 
O'OIO 

0'032 

o'oiS 

I-I3 

5-11 

9-67 
4378 

15-8 

4'3 
9'2 

0-009 

0'49S 

Spring  water    . 

0*001 

0-013 

2  '49 

28-20   |    iro 

7'5     '  0-383 

Sea  water    .     . 

0*005 

0-165 

I975-6 

3898-7    48-9 

748-0 

0*033 

Shallow  well    . 

0-091 

0-126 

57 

18-5             2-0 

i  '4 

O'OOO 

River  water 

O'OOI 

0-059 

175 

II-I6 



6-0 

0-08  1 

In  order  to  form  an  opinion  of  the  purity  of  a  sample  of  water, 
the  results  of  analysis  should  be  considered  as  a  whole  and  in 
relation  to  one  another.  No  definite  rules  can  be  laid  down,  but 
the  following  general  directions  should  be  kept  in  mind. 

Contamination  with  animal  matter — sewage,  etc.: — increases  the 
amount  of  nitrogen,  especially  that  present  as  free  ammonia,  and 
of  chlorine.  Vegetable  matter  also  increases  the  amount  of  nitrogen 
but  not  of  chlorine,  and  in  this  case  the  amount  of  albuminoid 
ammonia  will  generally  be  much  greater  than  that  of  the  free 
ammonia.  Chlorine  may  be  derived  from  mineral  sources,  but 
in  that  case  the  amounts  of  free  and  albuminoid  ammonia  will 
both  be  low. 

Very  hard  waters  are  unsuitable  for  many  domestic  purposes, 
and  it  is  said  that  they  are  liable  to  cause  inflammation  in  young 
children  and  invalids  ;  but  they  are  not  harmful  to  healthy  adults. 

Analysis  of  several  waters  are  given  in  the  table  above.  On 
studying  the  figures  and  bearing  in  mind  these  directions,  it  will 
be  obvious  that  in  these  particular  specimens  the  shallow  well 


/ 


B. 


-Oxygen 


WATER  31 

water  is  polluted  with  animal  matter  and  the  river  water  contains 
some  vegetable  matter.  The  other  drinking  waters  are  apparently 
free  from  organic  contamination. 

The  Composition  of  Water.— Pure  water  does  not  con- 
duct the  electric  current.  If  a  small  quantity  of  a  mineral 
acid,  such  as  sulphuric  acid,  be  added  to  the  water  then  the 
current  will  pass  through  it,  but  the  water  is  decomposed  (p.  4). 
This  method  of  decomposition  is 
known  as  electrolysis;  it  is  con- 
veniently performed  in  an  apparatus 
of  the  form  shown  in  the  illustra- 
tion (Fig.  8).  The  acidulated  water 
is  poured  into  the  apparatus  by  the 
funnel  E  until  it  begins  to  run  out 
at  the  taps  C  and  D,  which  are  then 
closed.  An  electric  current  is  then 
passed  through  the  liquid  by  con- 
necting the  platinum  plates  (elec- 
trodes) A  and  B  to  the  two  ends 
of  a  battery.  Bubbles  of  gas 
immediately  rise  from  each  elec- 
trode and  accumulate  in  the  upper 
part  of  each  of  the  side  tubes. 
After  a  short  time  it  will  be  Kathode* 
observed  that  the  gas  in  one  tube 
is  greater  in  quantity  than  that  in 
the  other — in  fact,  it  will  be  exactly 
twice  as  much — and  this  proportion  FIG.  8. 

will  be  maintained  as  long  as  the  gases  continue  to  be  evolved. 
The  gas  in  the  tube  which  contains  the  smaller  amount  will 
cause  a  glowing  splinter  of  wood  to  burst  into  flame.  It  is 
oxygen.  That  in  the  other  tube  will  burn.  It  is  hydrogen.1 
Water  therefore  consists  of  hydrogen  and  oxygen  combined  in 
the  proportion  of  two  volumes  of  hydrogen  to  one  volume  of 
oxygen.  It  is  obvious  that  water  cannot  be  a  mixture  of  these 
two  gases,  as  it  is  totally  unlike  either  of  them. 

Further  proofs  of  the  composition  of  water  are  given  later 

(P-  35). 

1  Gk.  &8up,  water. 


CHAPTER  V 

HYDROGEN 

Preparation. — The  inflammable  gas  liberated  from  water  by 
electrolysis  can  be  obtained  more  conveniently  in  other  ways, 
the  more  important  of  which  may  be  grouped  in  two 
divisions. 

A.  From  water,  by  the  action  upon  it  of  various  metals. 

If  a  piece  of  sodium  about  the  size  of  a  small  pea  be 
thrown  upon  the  surface  of  water,  the  metal,  being  lighter  than 
water,  floats;  it  melts,  showing  that  heat  is  developed,  and 
assumes  a  spherical  shape ;  it  rolls  about  over  the  water  and 
gradually  dissolves.  If,  however,  the  sodium  be  placed  upon 
a  floating  filter  paper,  and  is  thereby  prevented  from  moving, 
and  consequently  from  being  cooled  by  contact  with  the  colder 
water,  the  sodium  will  apparently  burst  into  flame.  This  is 
the  flame  of  hydrogen  which  the  heat  of  the  reaction  is  now 
sufficient  to  ignite.  The  gas  may  readily  be  collected,  if  the 
sodium  be  wrapped  in  wire  gauze  and  held  under  the  water. 
A  still  more  convenient  method  is  to  dissolve  the  metal  in 
mercury,  forming  a  paste  known  as  sodium  amalgam.  The 
presence  of  the  mercury  makes  the  reaction  take  place  more 
slowly,  so  that  but  little  rise  in  temperature  occurs,  and 
its  weight  causes  the  amalgam  to  sink  to  the  bottom  of  the 
water. 

If  potassium  be  used,  it  behaves  in  a  similar  manner,  but 
more  heat  is  developed,  and  the  liberated  hydrogen  takes 
fire  even  while  the  metal  is  rolling  over  the  surface  of  the 
water. 


HYDROGEN 


33 


The  violet  colour  of  the  flame  is  due  to  the  presence  of 
vapour  of  potassium  (p.  96),  the  yellow  colour  of  the  flame 
in  the  previous  experiment  was  due  to  vapours  of  sodium 
(p.  80).  The  decomposition  of  water  is  also  effected  by 
calcium.  In  each  case  the  metal  combines  with  the  oxygen 
of  the  water,  forming  a  compound  which  dissolves  and  imparts 
to  the  water  a  "soapy"  taste  and  makes  it  alkaline.  The 
calcium  compound  is  not  very  soluble  and  largely  separates 
as  a  white  solid. 

The  metals  already  mentioned  decompose  water  at  ordinary 
temperature.  Others  do  so  when  the  temperature  is  raised. 
If  metallic  magnesium  is  boiled  with  water,  hydrogen  is 
liberated ;  the  reaction  is  assisted  by  the  presence  of  a  small 
quantity  of  magnesium  chloride  in  the  water. 

Decomposition  of  water  by  magnesium  may  also  be  carried 
out  by  passing  steam  over  the  heated  metal. 

Iron  decomposes  water  at  a  red  heat.  This  gives  a  cheap 
method  of  preparing  large  quantities  of  hydrogen.  Iron 
filings  are  placed  in  an  iron  tube  which  is  heated  to  redness 
in  a  furnace,  and  while  the  filings  are  red  hot,  the  steam  from 
boiling  water  is  passed  over  them. 

B.  From  acids  by  reaction  with  metals. 

Hydrogen  is  more  conveniently  prepared  by  the  action  of 
certain  metals  upon  a  class  of  substances  known  as  acids 
(Chap.  VII),  all  of  which  contain  hydrogen.  The  most  con- 
venient acids  to  use  are 
hydrochloric  acid  (spirit 
of  salt)  (p.  73)  and  sul- 
phuric acid  (oil  of  vitriol) 
(p.  91),  and  the  metals 
most  usually  employed 
are  zinc  and  iron. 

Zinc  is  the  more  suit- 
able metal,  as  iron  is 
always  very  impure,  and 
the  hydrogen  which  is 
given  off  when  it  acts  upon  acids  is  mixed  with  other  gases 
which  obscure  its  properties.  The  sulphuric  acid  must  be 

D 


FIG.  9. 


34     A  FOUNDATION   COURSE   IN   CHEMISTRY 

dilute ;  if  the  concentrated  acid  is  used  very  little  action 
takes  place  and  no  hydrogen  is  evolved  (p.  62). 

When  zinc  or  iron  acts  upon  acids,  the  metal  dissolves 
and  the  resulting  compounds  may  be  obtained  in  a  crystalline 
form  on  evaporation  of  the  solution  (p.  28). 

Other  metals,  such  as  aluminium  and  magnesium,  as  well 
as  those  which  decompose  water  at  ordinary  temperatures, 
might  be  used,  but  they  would  be  either  more  expensive 
than  zinc  or  iron,  or  the  reaction  would  not  be  so  easily 
controlled. 

The  Physical  Properties  of  Hydrogen. — It  is  the  lightest 
substance  known.  It  is  generally  used  as  the  standard  of 
density  for  gases.  By  this  we  mean  that  we  state  the  density 
of  a  gas  by  saying  how  many  times  a  given  volume  of  it  is 
heavier  than  an  equal  volume  of  hydrogen  under  the  same 
conditions  of  temperature  and  pressure.  A  litre  of  hydrogen 
weighs  0*0898  gram. 

Owing  to  its  extreme  lightness  it  is  used  for  inflating 
balloons,1  and  the  more  modern  dirigible  air-ships. 

Hydrogen  is  less  soluble  in  water  than  either  oxygen  or 
nitrogen  ;  100  volumes  of  water  dissolve  only  about  2  volumes 
of  hydrogen  at  15°  C. 

It  is  colourless,  odourless,  and  without  any  action  upon 
litmus.  It  is  not  poisonous. 

Hydrogen  has  been  liquefied  and  solidified.  Under  ordi- 
nary atmospheric  pressure  it  boils  at  about  —252°  C. 

Many  metals  have  the  power  of  absorbing  (occluding) 
hydrogen.  Iron,  when  heated,  takes  up  19  times  its  own 
volume  of  gas,  and  finely  divided  platinum  50  times  its  own 
volume. 

The  Chemical  Properties  of  Hydrogen.— It  combines 
readily  with  oxygen  and  with  chlorine  (p.  74).  It  is  a 
reducing  agent,  that  is,  it  will  take  oxygen  away  from 
substances  which  contain  that  element  in  a  state  of  com- 
bination. 

Experimental   demonstration  : — i.  If   a  jar   of   hydrogen 

1  Coal  gas,  density  about  eight  times  that  of  hydrogen,  is  used  for 
ordinary  balloons. 


HYDROGEN  *     35 

be  held  mouth  downwards  and  a  lighted  taper  be  intro- 
duced, the  gas  takes  fire  and  burns  at  the  mouth  of  the 
jar,  but  the  flame  of  the  taper  is  extinguished.  The 
taper  requires  oxygen  to  enable  it  to  burn,  while  inside 
the  jar  there  is  only  hydrogen,  with  which  the  material  of  the 
taper  does  not  combine. 

2.  If  a  jar  of  hydrogen  be  held  mouth  upwards,  and  a 
lighted  taper  applied,  the  flame  of  the  burning  gas  will  rapidly 
run  down  the  whole  length  of  the  jar,  owing  to  more  thorough 
mixing  with  air. 

3.  In  a  mixture  of  two  volumes  of  hydrogen  with  one  volume 
of  oxygen  the  combination  is  so  rapid  as  to  produce  violent 
explosion. 

The  explosion  of  hydrogen  with  oxygen  yields  a  proof  of 
the  composition  of  water  by  volume.  If  the  gases,  in  the  pro- 
portion of  two  volumes  of  hydrogen  to  one  of  oxygen,  be 
mixed  in  a  tube  over  mercury  and  exploded  by  an  electric 
spark,  they  entirely  disappear  and  a  small  globule  of  water  is 
the  only  product. 

4.  When  dry  hydrogen  gas  is  passed  over  heated  copper 
oxide,  it  combines  with  the  oxygen,  and  water  and  metallic 
copper  are  produced. 

This  experiment  enables  us  to  estimate  directly  the  compo- 
sition of  water  by  weight.  The  water  formed  during  the 
reaction  is  collected  and  weighed,  the  loss  in  weight  of  the 
copper  oxide  is  the  weight  of  the  oxygen  present  in  the  water, 
and  the  difference  between  these  two  weights  is  the  weight  of 
hydrogen  used.  By  this  means  it  can  be  shown  that  hydrogen 
combines  with  oxygen  in  the  proportion  of  i  to  8  by  weight. 
This  is  the  same  as  2  to  i  by  volume,  for  oxygen  is  16  times 
as  dense  as  hydrogen. 

All  substances  which  contain  hydrogen  yield  water  as  a 
product  of  combustion.  This  can  readily  be  proved  in  the 
case  of  a  candle  or  gas-flame  by  holding  over  it  a  cold  glass 
vessel,  such  as  a  clean  dry  beaker.  The  surface  of  the  beaker 
will  be  covered  immediately  with  a  film  of  dew.  Rooms  in 
which  much  coal-gas  is  burnt  (coal-gas  contains  hydrogen) 
show  the  presence  of  water-vapour  in  the  air  by  a  copious 


36     A  FOUNDATION   COURSE    IN  CHEMISTRY 

deposit  upon  the  window-panes,  particularly  in  winter  time. 
Water-vapour  in  considerable  quantities  is  also  present  in 
respired  air.  The  heat  evolved  during  the  combustion  of 
hydrogen  is  often  utilised.  Most  of  the  substances  we 
use  as  fuels  (petroleum,  coal-gas,  etc.)  contain  hydrogen 
(p.  142). 


CHAPTER  VI 

GENERAL   PRINCIPLES 

Nomenclature. — Some  of  the  chemical  elements,  such  as 
sulphur  and  iron,  have  been  known  from  time  immemorial,  and 
their  colloquial  names  are  often  used  in  chemistry.  Lan- 
guages, however,  differ  greatly,  and  in  order  to  obtain  a 
universal  notation  the  Latin  names  for  these  elements,  when 
such  names  exist,  are  usually  employed  for  the  purposes  of 
symbolic  notation  (p.  39).  Elements  more  recently  dis- 
covered have  in  some  cases  received  names  descriptive  of 
their  more  striking  and  obvious  properties.  Chlorine,1  for 
example,  was  so  'called  because  the  gas  exhibits  a  greenish- 
yellow  colour;  bromine,'2  because  of  its  objectionable  and 
powerful  odour ;  chromium,,3  because  its  compounds  exhibit  a 
great  variety  of  colouring. 

The  Latin  names  for  metals  generally  ended  in  "  urn  " ;  so 
when  a  substance  of  this  kind  was  prepared  from  potash — 
which  is  simply  potashes  (p.  95) — it  was  called,  in  English, 
"  potassium." 4  Similarly,  the  metal  obtained  from  soda  was 
called  sodium,  and  so  on. 

Some  chemical  compounds,  such  as  water,  salt,  etc.,  have 
of  necessity  been  known  throughout  all  history,  and  in  every 
language  they  are  still  popularly  called  by  names  given 
them  long  ago.  These  names,  however,  are  not  generally 

1  Gk.  x\o)p6s,  greenish  yellow.     Cp.  chlorophyll,  literally  leaf  green. 
Gk.  <f>v\\oi',  a  leaf. 

2  Gk.  jSpw/toy,  a  stink. 

3  Gk.  XW"«>  colour.     Cp.  chromatic. 

4  Some  of  the  so-called  Latin  names  are,  of  course,  merely  Latinised 
forms  of  English  words,  others  are,  as  shown,  Latinised  forms  of  Greek 
words. 


38     A   FOUNDATION   COURSE   IN   CHEMISTRY 

used  in  chemistry  because  they  tell  us  nothing  about  the 
substances  they  refer  to.  It  has  "been  found  more  con- 
venient to  use  names  which  show  what  the  compounds  are 
composed  of,  and  a  scientific  system  has  been  invented  for  the 
purpose. 

A  compound  must  contain  at  least  two  elements,  and  the 
name  of  the  compound  is  made  up  from  the  names  of  both 
constituents.  Such  names  therefore  generally  consist  of  two 
words.  When  the  substance  is  composed  of  two  elements 
only  (a  binary  compound),  one  of  the  words  ends  in  "  ide." 
Thus  the  chemical  name  for  water  is  oxide  of  hydrogen, 
because  it  is  a  compound  of  oxygen  and  hydrogen ;  the 
chemical  name  for  common  salt  is  chloride  of  sodium,  because 
it  is  a  compound  of  chlorine  and  sodium.  When  sulphur  and 
copper  combine  together,  the  compound  is  called  sulphide 
of  copper.  The  word  "  of"  is  frequently  omitted.  We  may 
say  more  shortly,  hydrogen  oxide,  sodium  chloride,  copper 
sulphide. 

In  some  cases,  two  different  compounds  can  be  obtained 
from  the  same  two  elements.  They  are  distinguished  by 
the  terminations  ous  and  if.  The  element  iron  forms  two 
compounds  with  the  element  chlorine.  One  of  these  contains 
59-9  per  cent,  of  chlorine;  the  other  contains  65*5  per  cent. 
The  former  is  called  ferrous l  chloride,  and  the  latter  ferr/V1 
chloride.  The  universal  rule  is  that  the  name  of  the  com- 
pound which  contains  a  smaller  proportion  of  oxygen,  chlorine, 
sulphur,  etc.,  ends  in  "  ous,"  and  that  of  the  compound  which 
contains  the  larger  ends  in  "  ic." 

When  there  are  more  than  two  compounds  of  the  same 
two  elements  we  resort  to  the  use  of  prefixes.  In  the  case  of 
nitrogen  and  oxygen,  no  less  than  five  different  compounds 
are  known.  They  are  called  respectively,  nitrogen  monoxide, 
nitrogen  dioxide,  nitrogen  trioxide,  nitrogen  tetroxide,  and 
nitrogen  pentoxide,  because  for  a  given  quantity  of  nitrogen 
the  second  contains  twice  as  much  oxygen  as  the  first,  the  third 

1  Latin,  fernim,  iron.  The  older  names  of  these  compounds  are 
occasionally  used  ;  ferrous  chloride  being  called  iron  protochloride,  and 
ferric  chloride,  iron  perchloride. 


GENERAL   PRINCIPLES  39 

three  times  as  much,  and  so  on.1     The  prefixes  mono,  di,  tri,   - 
tetra,  and  penta  are  derived  from  the  Greek  words  for  single, 
two,  three,  four,  and  five. 

Symbolic  Notation. — In  order  to  economise  time  and 
labour,  and  for  more  important  reasons  which  will  be  adduced 
presently,  it  is  convenient  to  indicate  the  elements  by  symbols 
instead  of  writing  their  names  in  full.  The  symbols  commonly 
used  are  the  initial  letters  of  the  names  of  the  elements  ;  thus, 
H  stands  for  hydrogen,  O  for  oxygen,  N  for  nitrogen.2  When 
two  or  more  elements  have  the  same  initial,  that  letter  can 
only  be  used  for  one  of  them,  and  the  first  two  letters  of  their 
names  are  used  for  the  others.  Thus  C  stands  for  carbon,  Ca 
for  calcium,  Co  for  cobalt,  Cu  for  copper.3  Similarly,  since  S 
is  used  as  the  symbol  for  sulphur  it  cannot  also  be  used  for 
sodium.  This  element  has  had  the  Latinised  name  Natrium 
given  to  it,  and  we  use  its  first  two  letters,  Na,  to  represent 
sodium. 

When  a  single  letter  is  used  as  a  symbol,  it  is  always  a 
capital ;  when  two  letters  are  used,  the  first  is  a  capital  and  the 
second  a  small  letter.  Co  stands  for  cobalt,  but  CO  for  a 
compound  of  carbon  and  oxygen.  A  list  of  the  names  of  the 
known  elements  and  the  symbols  which  have  been  adopted  for 
each  will  be  found  in  the  appendix  (p.  216). 

Not  only  elements,  but  compounds  may  be  briefly  indicated 
by  means  of  this  symbolic  notation.  It  is  only  necessary  to 
write  next  to  one  another  the  symbols  for  each  element  in  the 
compound.  For  oxide  of  copper  we  put  CuO,  for  chloride 
of  sodium  NaCl,  for  sulphide  of  iron  FeS,  and  so  on.4  It 
will  be  noticed  that  this  method  has  not  only  the  merit  of 
brevity,  but  it  shows  the  composition  of  a  substance  even 
more  clearly  than  the  name  written  in  full.  It  will  presently 

1  These  names  also  contain  a  reference  to  the  fact  that  the  first  of  the 
compounds  contains  one  "  atom  "  of  oxygen  in  the  molecule. 

2  The  French  and  Italians  use  the  names  Azote  and  Azoto  respectively 
for  this  element,  and  the  symbol  Az.     Azote  is  from  the  Greek  fat,  life, 
and  a,  a  privative  particle  expressing  want  or  absence.     It  is  that  portion 
of  the  atmosphere  which  will  not  support  life. 

3  Latin,  cupriim. 

4  This  much  simplified  statement  will  receive  important  qualifications 
later. 


40    A  FOUNDATION   COURSE   IN  CHEMISTRY 

be  shown  that  it  has  other  and  more  important  advantages 
as  well. 

Laws  of  Chemical  Combination. — It  was  pointed  out 
(p.  3 1)  that  water  consists  of  hydrogen  and  oxygen.  It  is  never 
composed  of  hydrogen  and  sulphur,  or  of  oxygen  and  nitrogen, 
or  of  anything  else,  but  always  hydrogen  and  oxygen;  and 
that  these  two  elements  are  always  present  in  the  proportion  of 
two  volumes  of  the  former  to  one  of  the  latter.  Owing  to  the 
difference  in  the  density  of  the  gases,  the  proportions  by  weight 
are  one  part  of  hydrogen  to  eight  of  oxygen. 

When  hydrogen  burns  in  air  it  unites  with  oxygen  in  the 
proportions  mentioned  and  forms  water.  Hydrogen  can  unite 
with  sulphur  and  with  other  elements,  but  the  products  are 
not  water.  Hydrogen  may  unite  with  oxygen  in  a  different 
proportion,  but  the  product  is  not  water.  Similar  statements 
may  be  made  in  regard  to  every  chemical  compound.  In 
short,  we  may  say  that  each  chemical  compound  always  con- 
tains the  same  elements,  and  these  elements  are  always  present 
in  exactly  the  same  proportions  by  weight.  This  universal 
truth  is  called  the  Law  of  Definite  or  Constant  Proportions? 

The  decomposition  of  calcium  carbonate  (p.  65)  provides 
data  for  another  example  of  this  same  truth.  When  TOO  grams 
of  the  pure  substance  are  heated  they  yield  exactly  56  grams 
of  calcium  oxide  (lime)  and  44  grams  of  carbon  dioxide.  It 
can  be  further  shown  that  the  calcium  oxide  contains  exactly 
40  grams  of  calcium  and  16  grams  of  oxygen,  and  that  the 
carbon  dioxide  contains  exactly  12  grams  of  carbon  and  32 
grams  of  oxygen.  It  is  clear,  therefore,  that  the  100  grams  of 
calcium  carbonate  contained  in  all  40  grams  of  calcium,  12 
grams  of  carbon,  and  48  grams  of  oxygen.  These  proportions 
never  vary. 

In  examining  various  compounds  we  come  across  many 
instances  of  bodies  apparently,  totally  distinct,  but  composed  of 
the  same  elements.  Analysis  shows  that  in  these  cases  the 
elements  are  present  in  different  proportions  by  weight. 

1  Note  that  a  "Natural  Law"  bears  no  resemblance  whatever  to  an 
Act  of  Parliament — it  includes  no  element  of  compulsion.  It  is  simply 
a  condensed  statement  of  a  regularity  deduced  from  the  results  of  many 
experiments. 


GENERAL   PRINCIPLES  41 

Thus,  when  mercury  is  ground  in  a  mortar  with  a  small 
quantity  of  iodine  moistened  with  methylated  spirit,  a  dull 
green  powder  (mercurous  iodide)  is  produced.  On  increasing 
the  amount  of  iodine,  and  continuing  the  grinding,  a  bright  red 
compound  (mercuric  iodide)  is  formed. 

The  combustion  of  carbon  in  excess  of  oxygen  gives  rise 
to  the  formation  of  carbon  dioxide,  but  if  this  gas  is  passed 
over  red  hot  carbon  another  oxide  of  carbon  (carbon  monoxide) 
is  produced. 

There  are  five  compounds  of  nitrogen  with  oxygen. 

Analyses  of  100  parts  by  weight  of  these  compounds  of 
mercury,  carbon,  and  nitrogen  give  the  following  results : — 

Mercurous  iodide  :  mercury,  6n6  ;  iodine,  38-84. 
Mercuric  iodide  :  mercury,  44*05  ;  iodine,  5 5 -95. 
Carbon  monoxide:  carbon,  42*85  ;  oxygen,  57*15. 
Carbon  dioxide  :  carbon,  27*27.;  oxygen,  7272. 
Nitrous  oxide  :    nitrogen,  63-63  ;  oxygen,  36-36. 
Nitric  oxide:  nitrogen,  46-6;  oxygen,  53*3. 
Nitrogen  trioxide  :  nitrogen,  36*84;  oxygen,  63-16. 
Nitrogen  peroxide :  nitrogen,  30*43;  oxygen,  69*57. 
Nitrogen  pentoxide  :  nitrogen,  25*92  ;  oxygen,  74*08. 

These  numbers  do  not  appear  to  have  any  definite  relation 
to  one  another.  But  if  we  calculate  from  them  the  amounts  of 
one  element  combining  with  a  constant  weight  of  the  other  we 
obtain  results  of  great  importance.  They  may  be  expressed  as 
follows  : — 

Mercurous  iodide  :  mercury,  i  ;  iodine,  0*635. 
Mercuric  iodide  :  mercury,  i  ;  iodine,  1*27. 
Carbon  monoxide:  carbon,  i  ;  oxygen,  1*3. 
Carbon  dioxide  :  carbon,  i  ;  oxygen,  2 '6. 
Oxides  of  nitrogen  (i)  :  nitrogen,  i ;  oxygen,  0-57. 
„  „  (2)  :  nitrogen,  i  ;  oxygen,  1*14. 

„  „  (3):  nitrogen,  i;  oxygen,  1*71. 

„  „  (4)  :  nitrogen,  i ;  oxygen,  2*28. 

(5)  :  nitrogen,  i  ;  oxygen,  2*85. 

These  figures  show  that  the  weights  of  iodine  combining 


42     A  FOUNDATION   COURSE   IN  CHEMISTRY 

with  a  fixed  weight  of  mercury  are  in  the  proportion  i  to  2  ; 
that  the  weights  of  oxygen  combining  with  a  fixed  weight  of 
carbon  are  also  in  the  proportion  i  to  2,  and  that  in  the  case 
of  the  oxides  of  nitrogen,  a  fixed  weight  of  nitrogen  unites 
with  various  weights  of  oxygen  which  are  in  the  proportions  i, 

2,  3.  4,  5- 

The  simple  relationship  here  shown  is  not  accidental  nor 
confined  to  the  cases  mentioned  ;  it  is  a  universal  truth  which 
is  generally  condensed  into  the  following  statement. 

If  any  two  elements,  A  and  B,  combine  in  more  than  one 
proportion  by  weight,  and  if  we  consider  a  fixed  weight  of  one 
of  them  A,  then  the  different  weights  of  B  which  combine  with 
this  fixed  weight  of  A  bear  a  simple  relation  to  one  another ; 
i.e.  they  stand  to  one  another  in  a  ratio  always  capable  of 
being  expressed  by  whole  numbers,  which  are  generally  small. 

This  statement  is  known  as  The  Law  of  Multiple  Pro- 
portions. 

The  proportions  by  weight  in  which  elements  combine  also 
show  another  important  relationship.  For  illustration  we  will 
take  the  elements  hydrogen,  oxygen,  chlorine,  and  zinc, 
although  any  other  elements  would  do  equally  well. 

When  hydrogen  burns  in  oxygen,  the  elements  combine  in 
the  proportion  by  weight  of  one  part  of  hydrogen  to  eight  of 
oxygen.  These  amounts  are  said  to  be  equivalent  to  one 
another.  Also  when  hydrogen  combines  with  chlorine  it  does 
so  in  the  proportion  by  weight  of  one  part  to  35*5  of  chlorine, 
and  these  are  said  to  be  equivalent  to  one  another. 

Moreover,  because  eight  parts  by  weight  of  oxygen  and 
35-5  of  chlorine  each  combine  with  one  part  by  weight  of 
hydrogen,  they  are  also  said  to  be  equivalent. 

Zinc  combines  with  both  oxygen  and  chlorine,  and  will 
displace  hydrogen  from  some  of  its  compounds.  The  pro- 
portions are — 

Zinc  with  oxygen  :  zinc,  32-5  ;  oxygen,  8. 
Zinc  with  chlorine  :  zinc,  32*5  ;  chlorine,  35*5. 

And  when  zinc  displaces  hydrogen,   32-5  parts  by  weight  of 
zinc  always  displace  one  part  by  weight  of  hydrogen. 


GENERAL   PRINCIPLES  43 

It  will  be  seen  that  the  relation  between  the  weights  of 
hydrogen,  oxygen,  and  chlorine  are  the  same  as  before,  and 
each  of  them  is  equivalent  to  32-5  parts  by  weight  of  zinc. 

Of  course  we  could  state  what  weights  of  any  two  elements 
are  equivalent  to  one  another  independent  of  any  general  con- 
nection, but  for  the  sake  of  uniformity  we  compare  them  all  with 
hydrogen  or  oxygen,  since  nearly  every  element  will  combine 
with  one  or  other  of  these.  We  say  the  equivalent  weight  of 
an  element  is  that  amount  by  weight  which  will  combine  with 
or  displace  from  its  compounds  one  part  by  weight  of  hydrogen 
or  eight  parts  by  weight  of  oxygen.1 

The  Atomic  Theory. — That  elements  combine  according 
to  the  laws  of  definite  and  multiple  proportions  is  beyond 
dispute.  In  the  absence  of  any  certain  knowledge,  Dalton 
(1808)  revived  an  ancient  hypothesis  as  to  the  nature  of  matter, 
to  explain  why  they  do  so.  He  suggested  that  matter  consists 
ultimately  of  minute  particles,  and  that  chemical  action  takes 
place  between  these  particles,  which  are  indivisible  and  have 
definite  weights.  These  particles  he  called  atoms?  The 
atoms  of  any  one  element  are  all  of  equal  weight  and  are  alike 
in  every  respect,  but  differ  from  those  of  any  other  element. 

This  hypothesis  (or  supposition)  has  never  been  actually 
proved,  but  it  accords  with  all  known  facts ;  it  has  therefore 
acquired  a  very  high  degree  of  probability  and  is  universally 
adopted.  It  is  known  as  the  Atomic  Theory. 

The  atoms  are  very  minute.  Their  absolute  weights 
cannot  therefore  be  determined,  but  it  is  obvious  that  they 
must  bear  a  relation  to  each  other  very  closely  connected  with 
the  equivalent  weights. 

As  a  rule  the  atoms  do  not  exist  singly  but  in  groups,  i.e.  in 
combination  with  each  other.  These  groups  are  called  mole- 
cules? The  molecules  of  an  element  are  composed  of  atoms 
which  are  all  of  one  kind.4  In  the  molecule  of  a  compound 
the  atoms  are  of  two  or  more  different  kinds. 

1  If  one  element  combines  with  another  in  more  proportions  than  one, 
it  has  more  than  one  equivalent. 

2  Greek,  STO^OS,  indivisible. 

3  Latin,  moles,  a  heap. 

4  Some  elements  have  but  one  atom  to  the  molecule. 


44     A  FOUNDATION   COURSE   IN  CHEMISTRY 

The  symbols  which  we  have  adopted  to  represent  the 
elements  can  now  be  given  a  more  definite  meaning.  Na, 
for  instance,  is  not  only  a  short  and  convenient  way  of  writing 
"  Sodium," but  represents  one  atom  of  that  element;  similarly 
for  the  symbol  of  every  other  element. 

It  will  be  shown  later  (p.  75)  that  the  molecule  of 
hydrogen  consists  of  two  atoms,  and  that  the  molecule  of 
water  is  composed  of  two  atoms  of  hydrogen  and  one  atom  of 
oxygen.  As  we  know  that  the  proportion  by  weight  in  which 
these  elements  combine  is  i  to  8,  it  follows  that  the  ^tom 
of  oxygen  is  16  times  as  heavy  as  the  atom  of  hydrogen. 
We  take  the  atom  of  hydrogen  as  the  standard  and  compare 
the  atoms  of  all  other  elements  with  it.  The  number  so 
obtained  is  called  the  atomic  weight.  The  atomic  weight  of 
oxygen  therefore  is  16.  This  is  twice  the  equivalent  of 
oxygen,  and  every  element  one  atom  of  which  combines  with 
two  atoms  of  hydrogen  will  have  the  atomic  weight  double  of 
the  equivalent. 

It  will  also  be  shown  that  the  molecule  of  hydrochloric 
acid  (p.  75)  consists  of  one  atom  of  hydrogen  and  one  atom 
of  chlorine,  and  as  the  proportion  by  weight  is  i  to  35-5  the 
atomic  weight  of  chlorine  is  35*5.  This  is  the  same  as  the 
equivalent,  because  one  atom  of  chlorine  combines  with  one 
atom  of  hydrogen. 

In  all  cases  the  equivalent  of  an  element  is  either  equal  to 
the  atomic  weight,  or  is  a  very  simple  sub-multiple  of  it. 

The  atomic  weights  are  often  referred  to  as  combining 
weights^  as  they  express  the  fixed  proportions  by  weight  in 
which  elements  combine  with  one  another. 

The  formulae  used  to  represent  compounds  imply  more  than 
is  shown  above.  Thus,  the  composition  of  water  is  expressed 
by  the  formula  H2O,  which  shows  not  only  that  the  compound 
contains  hydrogen  and  oxygen  in  the  proportion  of  2  volumes 
of  the  former  to  i  of  the  latter,  but  that  the  molecule  of 
water  contains  two  atoms  of  hydrogen  and  one  of  oxygen,  and, 
knowing  the  atomic  weights,  that  two  parts  by  weight  of 
hydrogen  have  combined  with  sixteen  of  oxygen. 

Similarly  the  molecule  of  sodium  chloride  is  composed  of 


GENERAL   PRINCIPLES  45 

one  atom  of  sodium  and  one  atom  of  chlorine.  The  formula 
NaCl  is  therefore  used  to  represent  this  molecule. 

The  sum  of  the  weights  of  the  atoms  in  a  molecule  is  the 
weight  of  the  molecule  uiJ^rms^of  one  a^om  of  hydrogen,  i.e. 
it  is  the  molecular  weight  of  the  compound.  Thus,  the  atomic 
weight  of  sodium  is  23,  and  that  of  chlorine  35*5,  therefore 
the  molecular  weight  of  sodium  chloride  is  23  +  35-5,  i.e.  58-5. 
The  molecular  weight  of  carbon  monoxide,  CO,  is  12  +  16, 
i.e.  28 ;  that  of  carbon  dioxide,  CO2,  is  12  +  (16  X  2),  i.e.  44. 

The  molecular  weights  of  all  compounds,  however  complex, 
may  be  found  from  their  known  formulae  in  a  similar  manner, 
viz.  by  adding  together  the  atomic  weights  of  the  elements. 

Thus,  the  molecular  weight  of  calcium  carbonate  CaCO3  is 
found  thus : — 

Atomic 
Element,    weight.  Multiple.       Total. 

Ca,     Calcium    40        x      i    =    4° 

C,      Carbon       12        x      i    =    12    100 

3O,  Oxygen      16       X      3    =    4& 

The  molecular  weight  of  the  compound  is  100. 

The  Quantitative  Nature  ef  Chemistry.— The  importance 
of  the  facts  enunciated  above  cannot  be  over  estimated 
Without  these  quantitative  relationships  chemistry  in  the 
modern  sense  would  be  impossible.  We  should  never  be  able 
to  tell  whether  a  substance  was  pure,  or,  if  impure,  how  much 
impurity  it  contained ;  we  should  not  even  be  able  to  say  how 
much  of  any  constituent  it  ought  to  contain.  The  necessity 
of  being  able  to  undertake  all  the  simpler  calculations  of 
chemistry  will  therefore  be  obvious. 

If  we  wish  to  find  the  percentage  composition  of  a  com- 
pound, that  is,  the  amount  by  weight  of  each  element  in  100 
parts  by  weight  of  the  compound,  we  proceed  as  follows  : — 

We  write  down  the  formula  (say  that  of  nitrate  of  soda)  and 
then  find  the  molecular  weight. 


Na  =  23 

N    =  14 

30  =  16  x  3  =  48 


85,  the  molecular  weight. 


46     A  FOUNDATION   COURSE    IN   CHEMISTRY 

Thus  we  see  that  every  85  parts  by  weight  of  this  compound 
contain  23  of  sodium,  14  of  nitrogen,  and  48  of  oxygen. 

85  parts  by  weight  of  NaNO3  contain  23  of  Na. 
i  „  „  „  „      ||ofNa 


Similarly  the  percentage  of  nitrogen  is  *4  =  1  6-47 

*>5 

and  the  percentage  of  oxygen  4    X  I0°  =  56-47 

85 

lOO'OO 

In  like  manner  we  can  calculate  the  amount  of  each  element 
in  1  7-5,  or  123,  or  in  any  other  number  of  parts  by  weight  of 
the  compound  ;  the  difference  is  that  instead  of  multiplying  by 
ioo  we  must  multiply  by  the  number  given. 

For  example,  if  we  wish  to  find  the  amount  of  each 
element  in  59  parts  by  weight  of  potassium  bichromate 
(K2Cr207)  we  have  as  before 

Element.  Atomic  wt. 

K2      =      39        X      2     =       78) 
Cr2      =      52-5     x      2     =     105  1  295 
O7      =      16        x     7     =     112  j 

295  parts  by  weight  of  K2Cr2O7  contain  78  of  potassium. 

78 
"   295 

59         ,,  „  „  „     7-='5-6 


Similarly  the  weight  of  chromium  is  I05  x  59  __  21.0 

295 

and  the  weight  of  oxygen  is  IC2  x  59  =22-4 

295 


It  will  be  noticed  that  in  these  calculations  no  mention  is 
made  of  definite  quantities,  but  merely  of  proportions  or  parts 
by  weight.  It  is  obvious,  however,  that  the  results  of  our 


GENERAL   PRINCIPLES  47 

calculations  hold  in  any  system  of  weights  whatever.  Thus, 
59  pounds  of  potassium  bichromate  contain  15-6  pounds  of 
potassium,  21  pounds  of  chromium,  and  22*4  pounds  of  oxygen. 
Similarly,  59  grams  of  this  substance  contain  15*6  grams  of 
potassium,  21  grams  of  chromium,  and  22-4  grams  of  oxygen. 

Again,  suppose  it  were  required  to  find  how  many  pounds 
of  nitrogen  are  contained  in  i  cwt.  of  sulphate  of  ammonia, 
containing  5  per  cent,  of  impurity.  Since  there  are  5  pounds 
of  foreign  matter  in  100  pounds,  there  will  be  5  X  112-4-100 
=  5 '6  pounds  in  i  cwt,  so  that  we  have  only  112  —  5*6  =  106-4 
pounds  of  pure  sulphate  of  ammonia  in  i  cwt.  of  the  substance. 

The  problem,  therefore,  is  to  find  how  many  pounds  of 
nitrogen  are  contained  in  this  quantity.  The  formula  is 
(NH4)2  SO,.1 

N2  =  14  X  2     H8  =  i  X  8     S  =  32     O4  =  16  X  4 
=          28         +  8         +        32  +  64         =  132 

If  132  pounds  of  sulphate  of  ammonia  contain  28  pounds 

.    28  x  106-4 
nitrogen,  106*4  pounds  will  contain =  22-57  pounds. 

It  will  be  seen  that  calculations  of  this  kind  are  of  great 
importance  in  connection  with  the  practical  affairs  of  the 
farmer  or  of  any  other  business  man  who  has  to  employ 
chemical  materials,  artificial  manures,  paints,  cements,  etc. 

We  have  shown  how  to  find  the  percentage  composition  of 
a  substance  when  its  formula  is  known.  The  chemist  is  more 
often  called  upon  to  perform  the  reverse  operation,  and  from 
the  results  of  analyses,  which  it  is  customary  to  express  in 
percentages,  to  deduce  the  chemical  formula. 

A  substance  on  analysis  was  found  to  contain : 

Sodium     ...........     27 '06 

Nitrogen 16*47 

Oxygen 56-47 

lOO'OO 

It  is  required  to  find  its  formula. 

1  (NH4)2  is  equivalent  to  N2H8,  but  it  is  written  as  above  for  reasons 
given  later  (p.  126). 


48     A  FOUNDATION   COURSE   IN  CHEMISTRY 

Divide  each  of  the  percentages  by  the  atomic  weight  of 
its  element.     Thus  — 


_  =  ri76  -j='-'76  -=  3-5*9 

This  shows  that  the  number  of  atoms  of  each  element 
present  are  in  the  proportion 

Na,  1-176  N,  ri76  O,  3*529 

The  numbers  above  are  almost  exactly  in  the  ratio  of  i,  i, 
and  3,  and  the  formula  of  the  substance  is  NaNO;5  ;  it  is  sodium 
nitrate. 

Chemical  "  Equations."  —  The  substances  which  take  part  in 
a  chemical  reaction,  and  the  products  of  the  reaction  may  all 
be  represented  by  chemical  formulae,  so  that  formulae  may  be 
used  to  assist  in  the  representation  of  chemical  changes. 

Any  of  the  chemical  changes  previously  described  may  be 
represented  by  means  of  formulae.  For  instance,  (i)  the 
decomposition  of  oxide  of  mercury  (p.  19)  is  written  : 

HgO     ->     Hg     +     O 

Mercuric  Mercury.          Oxygen. 

oxide. 

The  combination  of  sulphur  with  iron  : 

(2)  Fe  -f  S  ->  FeS  (Ferrous  sulphide) 
The  decomposition  of  potassium  chlorate  : 

(3)  KC103   ->   KC1    +    30 

Potassium  Potassium 

chlorate.  chloride. 

The  interaction  of  lead  nitrate  and  potassium  sulphate 
when  their  solutions  are  mixed  : 


(4)  Pb(NO3)2   +   K2Sp4  ->  PbSO4  +    2KNO3 

Lead  nitrate.  Potassium  Lead  Potassium 

sulphate.  sulphate.  nitrate. 

These  expressions  are  called  .equations.  They  receive  this 
name  because  the  whole  weight  of  material  before  and  after 
the  action  must  be  identical.1  They  are  not  equations  in  the 

1  This,  of  course,  is  only  another  way  of  saying  that  in  any  chemical 
change  —  no  matter  how  complex  or  of  what  kind  —  the  total  quantity  of 
matter  remains  unaltered.  We  can  neither  create  nor  destroy  matter. 
This  universal  truth  is  called  the  Law  of  Conservation  of  Matter. 


GENERAL   PRINCIPLES  49 

algebraical  sense,  and  it  is  no  longer  the  invariable  custom  to 
write  the  sign  of  equality  (  =  )  between  the  two  sides,  but 
more  generally  an  arrow  ->  is  used  to  signify  the  direction  in 
which  the  reaction  takes  place.  The  equation  Fe  +  S  =  FeS 
should  be  read,  iron  +  sulphur  yield  or  produce  sulphide  of 
iron,  not  iron  4-  sulphur  equals  sulphide  of  iron. 

Equation  No.  4  represents  a  case  of  "  double  decomposi- 
tion," i.e.  a  reaction  in  which  two  substances  react,  exchange 
parts,  and  thus  produce  two  different  compounds. 

Perhaps  this  can  be  rendered  clearly  by  a  simple  diagram. 

Lead  Nitrate 


Potassium  Sulphate 

Substituting  the  formula  the  expression  appears  thus — 
Pb  (N03)2 


K2  SO4 

Equations,  however,  are  more  convenient  than  this  dia- 
grammatic form  for  representing  chemical  changes.  Especially 
is  this  the  case  when  the  changes  are  of  a  more  complete 
character.  For  instance,  to  indicate  the  action  of  hydro- 
chloric acid  upon  calcium  carbonate  by  a  diagram  would 
probably  prove  misleading,  but  the  change  is  easily  repre- 
sented by  an  equation,  thus : 

CaC03      +      2HC1     —     CaCl2     +     CO2     +     H2O 

Calcium  Hydrochloric  Calcium  Carbon  Water, 

carbonate.  acid.  chloride.  dioxide. 

A  little  practice  will  enable  any  one  who  is  familiar  with 
the  formulae  to  represent  all  kinds  of  chemical  changes  by 
equations.1 

The  equation  representing  the  action  of  calcium  carbonate 
on  hydrochloric  acid  illustrates  the  use  which  may  be  made  of 

1  Provided  also  that  the  chemistry  of  the  change  is  understood.  It  is 
easy  to  make  up  equations  which  "look  all  right"  but  which  do  not 
represent  any  chemical  reaction.  For  instance,  Pt  +  4.HC1  —>  PtCl4  -f-  2H3 
may  seem  quite  right,  but  such  a  reaction  does  not  take  place. 

£ 


50     A  FOUNDATION   COURSE   IN   CHEMISTRY 

equations.  They  not  only  have  the  qualitative  meaning  men- 
tioned above,  but  the  quantitative  significance  is  even  more 
important. 

They  represent  the  amounts  by  weight  of  the  materials 
reacting,  and  also  the  amounts  by  weight  of  the  products  of  the 
reaction.  In  the  case  referred  to,  the  equation  means  that  one 
molecule  of  calcium  carbonate  reacts  with  two  molecules  of 
hydrochloric  acid  to  form  one  molecule  of  each  of  the  com- 
pounds calcium  chloride,  carbon  dioxide,  and  water.  But 
the  molecular  weights  of  each  of  these  compounds  can  easily 
be  calculated  — 


CaCO3        H 

-     2HC1      - 

->    CaCl2 

+     C02     - 

f-    H20 

i  +  35*5 

40  +  12  +  48 

36JTXJ2 

4Q_-M; 

12   +  32 

2   +   16 

100 

73 

in 

~44~ 

"7F" 

We  now  see  that  TOO  parts  by  weight  of  calcium  carbonate 
react  with  73  parts  by  weight  of  hydrochloric  acid  and  yield 
in  parts  by  weight  of  calcium  chloride,  44  of  carbon  dioxide, 
and  1  8  of  water.  The  proportions  in  which  the  substances 
react  are  invariable,  and  so  are  the  relative  amounts  of  the 
products  of  the  reaction. 

To  find  out  how  much  acid  would  be  required  if  more  or 
less  than  100  parts  by  weight  (which  may  be  grams,  pounds, 
tons,  or  anything  else)  of  calcium  carbonate  are  employed,  and 
the  amounts  of  calcium  chloride  and  other  products  formed,  is 
a  simple  exercise  in  elementary  arithmetic. 

Valency.  —  It  will  be  shown  (p.  75)  that  one  atom  of 
chlorine  combines  with  one  atom  of  hydrogen.  In  water 
one  atom  of  oxygen  is  combined  with  two  atoms  of 
hydrogen,  and  in  ammonia  (p.  125)  one  atom  of  nitrogen  is 
combined  with  three  atoms  of  hydrogen.  The  elements 
chlorine,  oxygen,  and  nitrogen  are  said  to  differ  in  valency.1 
Chlorine  is  described  as  being  monovalent,  oxygen  as  divalent, 
and  nitrogen  in  ammonia  is  a  trivalent  element.  Similarly 
carbon  is  a  tetravalent  element,  for  marsh  gas  (p.  139)  is  found 

1  Latin,  valere^  to  be  worth. 


GENERAL   PRINCIPLES  51 

to  be  properly  represented  by  the  formula  CH4,  i.e.  one  atom 
of  carbon  is  combined  with  four  atoms  of  hydrogen.  A  mono- 
valent  or  monad  element  is  one,  of  which  one  atom  will  com- 
bine with  one  atom  of  hydrogen.  One  atom  of  a  divalent  or 
diad  element  will  combine  with  two  atoms  of  hydrogen;  it 
will  also  combine  with  two  atoms  of  any  other  monad  element 
with  which  it  forms  a  compound  or  with  one  atom  of  another 
diad  element.  Thus  one  atom  of  oxygen  will  not  only  combine 
with  two  atoms  of  hydrogen  but  also  with  two  atoms  of  potas- 
sium or  sodium,  which  are  also  monad  elements,  or  with 
one  atom  of  calcium  which  is  a  diad  element.  In  the  same 
way.  one  atom  of  a  tetravalent  or  tetrad  element  will  combine 
with  four  atoms  of  a  monad  element,  or  two  of  a  diad  element, 
or  one  atom  of  a  diad  element  and  two  of  a  monad,  etc. 
Compare,  for  example,  the  formulae — 

CH4,  CO2,  and  COC12. 

The  valency  of  an  element  is  measured  by  the  number  of 
atoms  of  hydrogen  with  which  one  of  its  atoms  will  unite. 

If,  however,  the  element  will  not  combine  with  hydrogen 
we  may  either  consider  the  number  of  atoms  of  oxygen  with 
which  one  atom  of  the  element  will  combine  or  determine  its 
valency  by  consideration  of  the  number  of  atoms  of  hydrogen 
one  of  its  atoms  will  displace. 

The  following  equations,  for  instance,  have  been  found  to 
be  correct — 

(1)  Na  +  H2O  ->  NaOH  +  H. 

Sodium  is  therefore  monovalent. 

(2)  Zn  +  2HCl->ZnCl2  +  H2. 

Zinc  is  therefore  divalent. 

(3)  Al-f3HCl->AlCl3  +  3H. 

Aluminium  is  therefore  trivalent. 

The  valency  of  an  element  is  in  reality  the  number  of 
atoms  of  hydrogen  which  one  of  its  atoms  is  worth>  either  in 
combination  or  replacement. 

The  valency  of  some  elements  is  not  always  the  same. 
Phosphorus,  for  example,  in  the  compound  phosphine,  PH3,  is 


52     A  FOUNDATION   COURSE   IN   CHEMISTRY 

trivalent,  while  in  phosphorus  pentoxide  P2O5  and  phosphoric 
acid  H3PO4  it  is  pentavalent.  Iron  forms  two  chlorides,  FeCl2 
and  FeCl3.  In  the  first  of  these  it  is  obviously  divalent,  in 
the  second,  trivalent.  The  valency  of  sulphur  shows  even 
greater  variation.  In  sulphuretted  hydrogen,  SH2,  sulphur  is 
obviously  diad ;  in  sulphur  dioxide,  SO2,  it  is  tetrad ;  while  in 
sulphur  trioxide,  SO3,  and  sulphuric  acid  it  is  hexad. 

Formulae  which  show  plainly  the  valency  of  the  elements 
in  a  compound  are  often  employed.    For  use  in  these  formulae — 

A  monad  element  would  be  represented  thus  :  Cl — ,  K — 
A  diad          „  „  „  _0-,-Ca- 

or  O=,  Ca— 

and  triad  and  tetrad  elements  and  those  of  higher  valency  in 
precisely  similar  manner ;  the  arrangement  of  the  lines  indicat- 
ing the  valency  is  of  no  importance  whatever. 

In  this  way  the  formulae  of  the  following  compounds  would 
appear  as  in  the  third  column  : — 

Caustic  soda  NaOH          Na— O— H 

Zinc  chloride  ZnCl2  Cl— Zn— Cl 

/Cl 
Aluminium  chloride  A1C13  Cl — Al<f 

Sulphur  dioxide  SO2  O=S=O 

.0 

Sulphur  trioxide  SO3  0=8^ 

^O 

Sulphuric  acid  H2SO4 

H— O/ 
O  O 

II  II 

Phosphorus  pentoxide        P2O5  P— O— P 

II  II 

O          O 


CHAPTER   VII 

OXIDES,   ACIDS,    BASES,    AND   SALTS 

IT  has  been  shown  (p.  16)  that  when  elements  combine  with 
oxygen  they  form  compounds  known  as  oxides,  and  that  on 
the  addition  of  water  some  of  these  oxides  pass  into  solution. 

Acids. — The  oxides  of  sulphur  and  phosphorus  obtained  by 
burning  the  elements  in  oxygen,  thus  dissolve  in  water,  and  in 
doing  so  impart  to  the  water  an  acid  reaction  (it  reddens  blue 
litmus).  It  is  not  strictly  accurate  to  say  that  these  oxides 
dissolve  in  water ;  they  combine  with  it  forming  soluble 
compounds.  Such  compounds  are  known  as  acids.  The 
combination  may  be  represented  by  an  equation.  Thus,  in 
the  case  of  sulphur,  the  oxide  SO2  combines  with  water  and 
forms  sulphurous  acid — 

SO2  +  H2O  ->  H2SO3  (sulphurous  acid). 

In  the  case  of  phosphorus,  the  oxide  P2O5  forms  phosphoric 
acid — 

P2O5  4-  sH2O  ->  2H3PO4  (phosphoric  acid). 

Sulphur  and  phosphorus  each  form  another  oxide  which  will 
also  combine  with  water  and  form  an  acid — 

SO3  +  H2O  ->  H2SO4  (sulphuric  acid). 
P4O6  4-  6H.O  ->  4H3PO3  (phosphorus  acid). 

Such  oxides  are  said  to  be  acidic,  and  there  is  a  large  number 
of  them.  The  oxides  of  carbon,  silicon,  boron,  arsenic,  and 
some  of  the  oxides  of  nitrogen  are  acidic  oxides  They 
combine  with  water  to  form  acids.  The  acids  have  a  sour 
taste  and  redden  blue  litmus. 


54     A  FOUNDATION   COURSE   IN  CHEMISTRY 

Bases. — If  now  certain  other  oxides  are  added  to  an  acid, 
it  loses  its  power  of  reddening  blue  litmus  solution ;  the  acid 
is  said  to  be  neutralised.  Oxides  which  have  the  power  of 
neutralising  an  acid  are  called  basic  oxides,  or  more  shortly, 
bases.  They  are  invariably  the  oxides  of  metallic  substances,1 
copper  oxide  CuO,  lead  oxide  PbO,  mercury  oxide  HgO, 
calcium  oxide  CaO,  magnesium  oxide  MgO,  iron  oxide  Fe2O3, 
sodium  oxide  Na2O,  potassium  oxide  K2O  are  basic  oxides. 

We  have,  therefore,  two  chief  classes  of  oxides — 

(a)  Acidic  oxides,  which  form  acids  with  water. 

(/3)  Basic  oxides,  which  will  neutralise  these  acids. 

Basic  oxides  also  combine  with  water.  The  compounds 
formed  are  called  hydroxides.2  Some  of  these  are  soluble  in 
water,  and  impart  to  the  water  the  power  of  restoring  the 
blue  colour  to  reddened  litmus.  They  are  said  to  be  alkaline. 

Potassium  oxide  K2O  combines  with  water. 

K2O  +  H,O  ->  2KOH 

The  compound  formed  is  very  soluble  in  water,  and  the 
solution  is  strongly  alkaline.  It  is  potassium  hydroxide,  also 
known  as  caustic  potash. 

Calcium  oxide  (quick  lime)  forms  calcium  hydroxide 
(slaked  'lime).  This  is  slightly  soluble  in  water,  giving  the 
solution  known  as  lime  water ;  it  is  alkaline. 

Iron  oxide,  Fe2O3,  and  copper  oxide,  CuO,  can  be  obtained 
combined  with  water.  The  compounds  are  not  soluble,  and 
therefore  no  alkalinity  is  noticeable. 

The  basic  oxides  can  therefore  be  divided  into  two  groups, 
those  which  are  soluble  and  those  which  are  insoluble  in 
water.  The  former  are  known  as  alkalis.  They  have  a 
"  soapy  "  taste,  and  turn  blue  litmus  red. 

Salts. — When  a  solution  of  an  alkali  is  added  to  that  of  an 
acid  they  yield  a  neutral  solution  if  the  quantity  of  each  is 
correct.  This  in  itself  would  not  show  that  anything  more 
than  mere  mixing  had  taken  place,  but  on  evaporating  nearly 


It  must  not  be  assumed  that  acidic  oxides  are  invariably  the  oxides  of 
metals.     Sorm 
The  term  "h 
generally  so  used. 


non-metals.     Some  metals,  e.g.  chromium,  manganese,  form  acidic  oxides. 
8  The  term  "  hydroxide  "  might  be  applied  also  to  the  acids,  but  it  is  not 


OXIDES,   ACIDS,   BASES,    AND   SALTS          55 

to  dry  ness,  a  substance  is  obtained  which  is  totally  different 
from  either  the  acid  or  the  alkali.  If,  for  example,  sulphuric 
acid  be  added  to  caustic  potash  solution,  until  neutral,  and  the 
solution  be  evaporated,  a  white  crystalline  solid  is  obtained. 
Analysis  shows  that  it  is  properly  represented  by  the  formula 
K2SO4 ;  it  is  known  as  potassium  sulphate. 

If  we  treat  sulphuric  acid  with  magnesium  oxide,  warming 
the  mixture  to  assist  solution,  on  evaporation  a  white  crystal- 
line solid  is  again  obtained.  This  is  magnesium  sulphate, 
MgSO4.1  It  will  be  seen,  therefore,  that  when  a  basic  oxide, 
whether  soluble  or  insoluble,  neutralises  an  acid,  another 
compound  is  formed.  Such  compounds  are  called  salts. 

The  reaction  in  the  first  case  is  represented  by  the 
equation — 

2KOH  +  H2SO4-»  K2SO4  +  2H2O 
that  in  the  second  case — 

H2S04  +  MgO  ->  MgS04  +  H20 

The  salt  may  be  conveniently  considered  as  arising  from 
the  combination  of  the  basic  and  acidic  oxides  with  elimination 
of  the  water  with  which  they  were  combined.  liases  combine 
with  acids  to  form  salts  ^  with  the  liberation  of  water.  We  have 
shown  the  formation  of  acids  from  acidic  oxides  and  water. 
There  are  several  acids  which  are  not  formed  in  this  way. 
Hydrochloric  acid  is  the  most  familiar  example.  The  formula 
of  this  compound  is  HC1.  It  is  formed  by  the  union  of 
hydrogen  and  chlorine,  and  contains  no  oxygen.  Its  solution 
in  water  possesses  all  the  properties  of  an  acid ;  it  has  a  sour 
taste,  reddens  litmus,  and  can  be  neutralised  by  a  base  such 
as  sodium  oxide  or  hydroxide,  when  it  forms  sodium  chloride 
(common  salt),  NaCl. 

Comparing  the  formula  of  a  salt  with  that  of  the  acid  from 
which  it  can  be  produced  we  notice  great  similarity,  thus — 

H2SO4  is  sulphuric  acid         Na2SO4  sodium  sulphate 
ZnSO4  zinc  sulphate  CaSO4  calcium  sulphate 

1  These  crystals  contain  water  of  crystallisation  (p.  29)  ;  they  have  the 
formula  MgSO4.7H8O. 


56     A   FOUNDATION   COURSE   IN   CHEMISTRY 

The  formulae  of  the  salts  formed  from  hydrochloric  acid 
show  a  like  similarity — 

HC1,  NaCl,  ZnCl2,  CaCl2 

According  to  these  formulae  an  acid  differs  from  its  salts 
in  that  in  the  latter  the  hydrogen  of  the  acid  is  replaced  by 
a  metal.  For  this  reason  it  is  often  convenient  to  look  upon 
the  acids  as  salts  of  hydrogen,  and  it  is  not  at  all  unusual  to 
find  sulphuric  acid  referred  to  as  hydrogen  sulphate,  hydro- 
chloric acid  as  hydrogen  chloride,  and  other  acids  in  corre- 
sponding manner. 

In  many  cases  this  replacement  of  hydrogen  can  be  per- 
formed directly.  Thus  if  zinc,  iron,  magnesium,  and  certain 
other  metals  are  treated  with  dilute  sulphuric  or  hydrochloric 
acid,  the  hydrogen  is  set  free  from  the  acid  and  the  metal 
takes  its  place — 

Zn    +      H2SO4       ->        ZnSO4      -f      H2 

Zinc.  Sulphuric  acid  Zinc  sulphate.  Hydrogen. 

(Hydrogen  sulphate). 

Mg     +      2HC1        ->         MgCl2      +      H2 

Magnesium.     Hydrochloric  acid  Magnesium  Hydrogen. 

(Hydrogen  chloride  )  chloride. 

The  properties  of  acids  we  have  now  found  are — 

(a)  They  have  a  sour  taste  and  redden  blue  litmus. 

(ft)  They  are  neutralised  by  alkalies  or  bases,  generally 
with  the  formation  of  a  salt  and  liberation  of  water. 

(y)  They  contain  hydrogen  which  can  be  replaced  by  a 
metal  forming  a  salt. 

In  a  previous  experiment  we  found  that  on  neutralising 
sulphuric  acid  with  caustic  potash,  potassium  sulphate,  K2SO4, 
was  formed.  If  we  take  the  same  amount  of  sulphuric  acid 
and  add  only  one-half  the  amount  of  caustic  potash  required 
to  neutralise  it,  we  obtain  on  evaporation  another  crystalline 
body,  which  analysis  proves  to  have  the  composition  repre- 
sented by  the  formula  KHSO4. 

H2SO4  +  KOH  ->  KHSO4  +  H2O 

This  is  obviously  sulphuric  acid  in  which  only  one-half 
of  the  hydrogen  has  been  replaced  by  potassium.  It  has  some 


OXIDES,   ACIDS,   BASES,   AND   SALTS  57 

of  the  properties  of  an  acid,  and  some  of  the  properties  of  a 
salt.  It  is  called  an  acid  salt.  The  actual  names  applied  to 
it  are  "acid  potassium  sulphate"  alluding  to  its  properties, 
or  "potassium  hydrogen  sulphate"  alluding  to  the  elements 
it  contains. 

If  we  try  a  similar  pair  of  experiments  with  hydrochloric 
acid  we  shall  obtain  the  same  compound  in  each  case,  potassium 
chloride,  KC1.  We  can  therefore  form  two  sulphates,  but 
only  one  chloride  of  potassium.  Acids  such  as  sulphuric  acid, 
forming  two  salts  of  potash,  are  said  to  be  dibasic.  Those 
which  like  hydrochloric  form  only  one  salt  are  said  to  be 
monobasic. 

The  basicity  of  an  acid  is  determined  by  the  number  of 
atoms  of  hydrogen  which  can  be  displaced  by  a  metal ;  thus 
HNO3,  nitric  acid,  is  monobasic;  H2CO3,  carbonic  acid,  is 
d/basic;  H3PO4,  orthophosphoric  acid,  is  //-/basic;  H4P207, 
pyrophosphoric  acid,  is  tetrabasic.  It  does  not  always  happen, 
however,  that  all  the  hydrogen  in  an  acid  is  replaceable. 
Thus  H3PO3,  phosphorous  acid,  is  dibasic,  because  only  two 
of  the  three  hydrogen  atoms  it  contains  are  replaceable  by  a 
metal.  H3PO2,  hypophosphorous  acid,  is  monobasic,  for  the 
only  salt  of  potash  which  can  be  prepared  from  it  is  KH2PO2 
(potassium  hypophosphite).  In  a  future  chapter  it  will  be 
shown  that  CH3COOH  (acetic  acid)  and  similar  acids  are  also 
monobasic. 

When  all  the  replaceable  hydrogen  in  an  acid  has  been 
replaced  by  a  metal,  the  salt  formed  is  called  the  normal 
salt  of  the  acid.  It  often  happens  that  the  normal  salt  is  also 
neutral,  but  this  is 'not  always  the  case.  For  instance,  the 
normal  sulphate  of  sodium  or  potassium  (Na2SO4  or  K2SO4) 
is  neutral;  the  normal  phosphate  (Na3PO4)  is  strongly 
alkaline ;  while  the  salt  Na2HPO4  is  neutral,  although  it  contains 
replaceable  hydrogen. 

The  following  is  perhaps  the  most  convenient  system  of 
nomenclature  for  such  salts  :— 

Na2SO4,  normal  sodium  sulphate.     (Neutral.) 
NaHSO4,  sodium  hydrogen  sulphate.     (Acid.) 


58     A  FOUNDATION   COURSE   IN   CHEMISTRY 

Na3PO4,  normal  sodium  phosphate.     (Alkaline.) 
Na2HPO4,  hydrogen  di-sodium  phosphate.     (Neutral.) 
NaH2PO4,  sodium  di-hydrogen  phosphate.     (Acid.) 

Other  oxides. — There  are  two  other  classes  of  oxides,  in 
addition  to  those  we  have  called  acidic  and  basic. 

(a)  Peroxides. 

When  lead  is  oxidised  in  the  air  or  in  oxygen  it  forms  the 
oxide  PbO.  This  is  a  basic  oxide.  But  this  oxide  of  lead 
can  be  further  oxidised  to  PbO2.  This  has  more  oxygen  in  it 
than  the  basic  oxide.  Such  oxides  are  called  peroxides.  When 
heated  they  give  off  part  of  their  oxygen  and  generally  leave  a 
residue  of  the  basic  oxide.  Other  well-known  peroxides  are 
barium  peroxide,  BaO2  (p.  19),  and  manganese  dioxide, 
MnO2. 

•  The  action  of  heat  upon  these  substances  is  shown  in  the 
following  equations :  — 

+  O 
-f  O2 
3MnO2->Mn3O4  +  O2 

When  treated  with  sulphuric  acid  peroxides  yield  oxygen — 
2MnO2  -f  2H2SO4->  2MnSO4  +  2H2O  -f  O2 

When  treated  with  hydrochloric  acid  they  cause  the  libera- 
tion of  chlorine,  as  the  oxygen  which  might  be  expected  to  be 
liberated  combines  with  the  hydrogen  of  some  of  the  hydro- 
chloric acid  and  liberates  the  chlorine  (p.  76)  — 

PbO2  -h  4HC1  ->  PbCl2  +  2H2O  +  C12. 

There  are  a  few  peroxides  which  behave  somewhat  differ- 
ently. The  peroxides  of  barium  and  sodium  when  treated 
with  dilute  sulphuric  acid  or  hydrochloric  acid  yield,  not  water 
and  oxygen,  but  hydrogen  peroxide,  H2O2 — 

BaO2  -f-  H2SO4  ->  BaSO4  -f-  H2O2. 

The  difference  between  these  two  classes  of  peroxides  may  be 
represented  by  graphic  formulae.  Those,  such  as  lead  peroxide, 
which  yield  oxygen  or  chlorine  when  treated  with  sulphuric  or 


OXIDES,   ACIDS,    BASES,   AND   SALTS  59 

hydrochloric  acid  contain  the  oxygen  doubly  linked  to  the  metal, 
thus:  Pb2^    .     Those  which  give  rise  to  the  formation  of  hydrogen 

peroxide  contain  the  group  — O— O —  ;  thus  sodium  peroxide  is 

/O 

Na— O— O— Na,  and  barium  peroxide  is  Ba<^   I  . 

•X) 

(b)  Carbon  monoxide,  CO,  nitric  oxide,  NO,  do  not  come 
into  the  above  groups,  for  they  are  neither  acid  nor  basic, 
nor  peroxides. 

The  above  classification  of  the  oxides,  while  useful  and 
even  necessary,  must  not  be  looked  upon  as  rigid.  Some 
basic  oxides  also  act  as  acidic  oxides  in  the  presence  of  strong 
bases,  while  some  acidic  oxides  have  peroxide  properties.1 

Hydrogen  Peroxide. — As  stated  above,  this  substance  is 
formed  when  barium  peroxide  is  treated  with  an  acid.  Sul- 
phuric acid  is  thee  most  convenient  as  it  precipitates  the 
insoluble  barium  sulphate ;  any  excess  of  sulphuric  acid  can 
be  removed  by  cautious  addition  of  barium  hydroxide, 
Ba(OH)2,  and  the  whole  of  the  sulphate  filtered  off.  The 
filtrate  is  a  dilute  solution  of  hydrogen  peroxide,  from  which 
the  pure  material  may  be  obtained  by  distillation  under 
reduced  pressure. 

It  is  a  powerful  oxidising  agent,  rapidly  giving  off  oxygen 
and  leaving  water.  Its  action  upon  potassium  iodide  is  shown 
in  the  equation — 

2KI  +  2HC1  +  H2O2->I*  +  2KC1  +  2H2O. 

With  chromic  acid,  H2CrO4,  it  forms  a  deep  blue  compound 
supposed  to  contain  the  oxide  Cr2O7,  but  this  decomposes  so 
rapidly  that  it  cannot  easily  be  analysed.  Hydrogen  peroxide 
may  also  act  as  a  reducing  agent  in  certain  special  cases. 

(a)  Upon  silver  oxide  the  action  is  as  follows  : — 

Ag2O  +  H2O,  ->  2Ag  +  H2O  +  O2 

1  Zinc  oxide,  ZnO,  and  aluminium  oxide  (A12O3)  will  dissolve  in  caustic 
soda  or  potash  forming  the  zincate  or  aluminate  of  soda  or  potash. 

MnO2,  manganese  dioxide,  CrO3,  chromium  trioxide,  both  of  which 
show  peroxide  properties,  will  combine  with  bases  and  form  salts. 


60     A  FOUNDATION   COURSE   IN  CHEMISTRY 

(/>)  Upon  potassium  permanganate  l — 
2KMnO4  -f  3H,,SO4  +  5H2O2  ->  2MnSO4  +  KoSO4  +  8H0O 

+  50, 

Its   oxidising   action   is   utilised    for    bleaching    delicate 
materials. 


APPENDIX  TO    CHAPTER  VII 

FURTHER  CONSIDERATION  OF  ACIDS,   BASES,  AND  SALTS 

A  PROPERTY  of  acids  which  provides  a  fairly  satisfactory  defini- 
tion is  their  power  of  forming  salts  with  caustic  soda  or  potash. 

An  acid  may  be  defined  as  a  body  of  the  formula  HnR  which 
will  react  with  caustic  potash  to  form  a  salt  of  the  formula  K,,R 
according  to  the  equation —  • 

HnR  +  wNaOH  -»  Na*R  +  «H2O 

where  n  represents  the  number  of  replaceable  hydrogen  atoms  in 
the  molecule  of  the  acid,  and  R  the  remainder  of  the  molecule. 

Thus  in  hydrochloric  acid  n  is  I  and  R  is  chlorine,  and  the 
equation  stands — 

HC1  +  NaOH  ->  NaCl  +  H2O 
With  sulphuric  acid,  n  is  2  and  R  is  SO4 — 

H2SO4  +  2NaOH  ->  Na2SO4  4-  2H2O 
With  phosphoric  acid,  n  is  3  and  R  is  PO4 — 

H3P04  +  3NaOH  ->  Na8PO4  +  3H2O 
With  acetic  acid,  n  is  I  and  R  is  CH3COO— 

CH3COO.H  +  NaOH  ->CH8COONa  +  H,O 

It  is  useless  to  define  an  acid  as  the  compound  formed  by  the 
union  of  an  acidic  acid  and  water,  as  there  are  many  acids  which 
contain  no  oxygen,  e.g.  HC1,  HBr.  The  property  of  reddening 
blue  litmus  is  shared  by  water  solutions  of  some  normal  salts  such 
as  CuSO4.  The  displacement  of  hydrogen  by  metals  will  also 

*  Hydrogen  peroxide  is  supplied  in  dilute  solutions  which  are  described 
by  the  amount  of  oxygen  they  will  give  off ;  thus  a  2O-volume  solution  of 
hydrogen  peroxide  is  one  which  will  give  off  20  times  its  own  volume  of 
oxygen. 


OXIDES,    ACIDS,   BASES,   AND    SALTS  61 

take  place  from  substances  of  a  totally  different  character,  such 
as  ammonia  and  caustic  alkalies,  thus — 

Dry  ammonia  gas  passed  over  heated  sodium  gives  sodamide 
and  hydrogen. 

2NH3  +  2Na->2NH2Na  +  H2 

Aluminium1  boiled  with  caustic  soda  solution  gives  sodium 
aluminate  and  hydrogen. 

2A1  +  6NaOH  ->  2Na3AlO3  +  3H2 

Electrolysis 2  and  Ionic  Dissociation. — Electrolysis  consists 
in  the  separation  of  the  components  of  a  dissolved  substance  by 
means  of  a  current  of  electricity  passed  through  the  solution.  It 
is  not  every  compound  which  can  be  so  decomposed  ;  those  which 
can  are  called  electrolytes.  The  apparatus  necessary  varies  in 
detail  with  the  nature  of  the  products,  but  that  used  for  the 
electrolysis  of  water  (p.  31)  contains  all  the  essential  parts.  An 
electric  battery  is  connected  by  wires  with  each  of  the  platinum 
plates.  These  plates  are  obviously  the  means  by  which  the  current 
enters  and  leaves  the  solution.  They  are  therefore  known  as 
electrodes.3  That  connected  with  the  zinc  of  the  battery  is  the 
negative  electrode  or  kathode,4  that  connected  with  the  carbon5 
the  positive  electrode  or  anode.6 

In  the  electrolysis  of  water  it  was  pointed  out  that  the  water 
alone  would  not  conduct  electricity.  There  are  no  signs  of  de- 
composition until  sulphuric  acid  is  added  ;  then  oxygen  is  given 
off  at  the  anode  and  hydrogen  at  the  kathode.  Had  we  used 
copper  sulphate  instead  of  sulphuric  acid  we  should  still  have  had 
oxygen  at  the  anode  as  before,  but  copper  at  the  kathode.  This 
copper  must  of  necessity  have  come  from  the  copper  sulphate,  not 
from  the  water,  and  this  being  so  the  student  will  probably  ask 
himself  whether  the  hydrogen  given  off  during  the  electrolysis  of 
water  does  not  come  after  all  from  the  acid.  In  a  sense  this  is 
actually  the  case. 

Independent  evidence  has  been  obtained  showing  that  when 
electrolytes  are  dissolved  in  water  they  undergo  a  species  of 
decomposition,  or,  more  strictly,  dissociation.  These  electrolytes 
are  precisely  those  compounds  which  may  take  part  in  double  decom- 
positions with  one  another — namely,  acids,  salts,  and  bases.  When 
sulphuric  acid  is  in  dilute  solution  in  water  it  is  largely  dissociated 

1  Metallic  zinc  behaves  in  a  similar  manner. 

2  Gk.  \vffis,  a  setting  free.  *  Gk.  oSov,  a  way  or  path. 

4  Gk.  /cara,  down.     Kathode  therefore  means  "the  way  down." 

5  It  has  been  assumed  a  simple  battery  is  employed  consisting  of  zinc 
and  carbon  plates.     Of  course  any  other  form   would  do  equally  well. 
The  essential  thing  is  that  the  kathode  is  the  electrode  connected  with  the 
negative  terminal  of  the  battery,  and  the  anode  that  connected  with  the 
positive  terminal. 

6  Gk.  oi/a,  up.      Anode  therefore  means  "  the  way  up,"  i.e.  against  the 
current. 


62     A  FOUNDATION   COURSE   IN  CHEMISTRY 

into  2H  l  and  SO4,  sodium  sulphate  into  2Na  and  SO4,  caustic 
soda  into  Na  and  OH.  According  to  modern  theory  these  por- 
tions of  the  dissociated  compound  carry  equal  and  opposite  charges 
of  electricity,  the  hydrogen  and  sodium  groups  being  charged 
positively,  and  the  SO4  and  OH  groups  negatively.  They  are 
known  as  ions.2  When  the  electrodes  are  connected  with  the 
terminals  of  the  battery,  the  ions  by  virtue  of  their  electric 
charges  are  directed  towards  the  electrode  oppositely  charged  ; 
thus  the  hydrogen,  sodium,  or  other  metallic  (positive)  ions  are 
directed  to  the  kathode  ;  the  SO4,  Cl,  or  other  negative  ions  to 
the  anode. 

We  can  now  see  what  probably  happens  when  a  current  is 
passed  through  water  containing  an  acid  or  a  salt  in  solution. 
The  current  does  not  decompose  the  acid  or  salt.  That  is  already 
dissociated  by  the  act  of  solution  ;  but  in  the  case  of  dilute 
sulphuric  acid,  the  hydrogen  ions  are  directed  to  the  kathode,  and 
there  form  molecules  of  hydrogen  which  accumulate  and  are  given 
off  as  hydrogen  gas.  The  SO4  ions  would  accumulate  at  the 
anode,  but  for  the  fact  that  SO4  reacts  with  the  water  to  form 
sulphuric  acid  and  oxygen.  The  sulphuric  acid  is  thus  again 
formed  and  again  undergoes  dissociation.  Indirectly,  therefore, 
the  hydrogen  and  oxygen  given  off  during  the  electrolysis  of 
water  really  come  from  the  water  although  the  sulphuric  acid  acts 
as  an  intermediary. 

The  case  of  copper  sulphate  is  identical.  The  salt  is  dis- 
sociated into  Cu  and  SO4.  Copper  is  deposited  on  the  kathode 
instead  of  hydrogen,3  and  the  SO4  reacts  with  water  at  the  anode 
to  form  sulphuric  acid  and  oxygen. 

If  sodium  sulphate  solution  be  electrolysed  hydrogen  is  evolved 
at  the  kathode,  oxygen  at  the  anode.  The  ions  of  sodium  sulphate 
are  2Na*  and  SO4".  But  the  sodium  which  might  accumulate  at 
the  kathode  reacts  with  water,  giving  caustic  soda  and  hydrogen, 
while  the  SO4  gives  as  before  H2SO4  and  oxygen.  If  the  solution 
be  made  purple  with  neutral  litmus  that  portion  surrounding  the 
kathode  will  be  turned  blue,  that  around  the  anode  red. 

From  the  foregoing  it  will  be  seen  that  the  characteristic  of  an 
acid  is  that  it  gives  hydrogen  ions  when  in  water  solution  ;  a 
soluble  basic  hydroxide  gives  hydroxyl  ions  (OH').  The  more 
dilute  the  solution  the  more  complete  this  ionisation  is. 

In  the  ionisation  of  acids  is  found  the  explanation  of  most  of 
their  properties.  It  gives  a  reason  for  the  frequent  liberation  of 
hydrogen  when  certain  metals  act  upon  acids  ;  and  shows  why 
concentrated  acids  behave  so  differently  from  the  same  acids 

1  These  groups  of  atoms  must  not  be  looked  upon  as  free  hydrogen,  or 
sodium,  etc. 

2  From   the    Gk.  fy/«,    I  go  j  the   word  may  be  taken  as  meaning 
"wanderers"  or  "travellers." 

3  A  small  quantity  of  hydrogen  is  also  given  off,  and  this  must  increase 
with  the  increasing  number  of  hydrogen  ions  due  to  the  continual  formation 
of  sulphuric  acid. 


OXIDES,   ACIDS,   BASES,   AND   SALTS          63 

diluted.  Hydrogen  cannot  be  obtained  from  concentrated  sul- 
phuric acid  by  the  action  of  zinc  or  any  other  metal,  nitric  acid 
will  only  yield  hydrogen  on  treatment  with  magnesium  when 
diluted  with  large  quantities  of  water,  and  liquid  anhydrous  hydro- 
chloric acid  obtained  by  condensing  the  gas  by  great  cold  and 
pressure  has  no  acid  properties.  It  also  explains  the  reactions 
(double  decompositions)  which  take  place  between  electrolytes  in 
solution.  For  instance,  when  solutions  of  sodium  sulphate  and 
barium  chloride  are  mixed  together  a  heavy  white  precipitate  is 
thrown  down. 

Now,  sodium  sulphate  is  ionised  into  2Na'  and  SO4" 


while  barium  chloride  is  ionised  into     Ba"  and  2CK 

In  these  circumstances  the  barium  ion  has'the  same  opportunity  of 
combining  with  the  SO4"  ion  as  the  sodium  ion  has,  and  barium 
sulphate  is  therefore  formed,  and,  being  insoluble,  is  removed 
from  the  solution  as  a  white  precipitate. 


CHAPTER  VIII 

,.     LIMESTONE 

Calcium  Carbonate. — All  forms  of  limestone,  including  chalk 
and  marble,  consist  essentially  of  one  chemical  compound 
known  as  calcium  carbonate,  or  carbonate  of  lime,  and  the 
differences  between  them  arise  chiefly  from  the  mode  of 
their  formation  and  their  structure.  In  marble  the  calcium 
carbonate  exists  as  a  mass  of  minute  crystals.1  Chalk  and 
most  limestones  are  not  crystalline,  but  yield  evidence  of  their 
organic  origin,  in  the  abundant  remains  of  shells,  coral,  etc., 
which,  in  the  case  of  many  limestones,  form  a  large  proportion 
of  the  rock.2 

In  the  British  Isles,  true  white  marble  is  not  found,  but 
chalk  and  limestones  exist  plentifully,  and  in  districts  where  they 
abound  the  industry  of  "  lime  burning,"  or  the  manufacture  of 
"  quick-lime,"  is  almost  invariably  to  be  found. 

Lime  Burning. — An  experiment  in  "lime  burning"  can 
easily  be  performed  by  the  aid  of  a  blow-pipe.  If  a  weighed 
piece  of  chalk,  limestone,  or  marble  be  heated  strongly  for  some 
time,  then  allowed  to  cool  and  again  weighed,  it  will  be  found 
to  have  decreased  considerably  in  weight.  If  the  heating  be 
continued,  the  loss  becomes  greater  until  the  chalk,  limestone, 
or  marble  has  lost  44  per  cent,  of  its  original  weight.  The  white 
substance  which  is  left  is  commercially  known  as  quick-lime. 
A  heavy  gas  is  given  off  during  the  process  ;  and  if  this  gas  were 
collected,  its  weight  would  be  found  to  be  exactly  equal  to  the 
loss  in  weight  suffered  by  the  calcium  carbonate  on  heating. 

1  Calcite  or  Iceland  Spar  is  another  highly  crystalline  form  of  calcium 
carbonate. 

2  The  shells  of  birds'-eggs,  coral,  pearls,  the  shells  of  shell  fish,  also 
consist  of  calcium  carbonate  with  varying  amounts  of  organic  material. 


LIMESTONE  65 

These  facts  show  that  the  term  "lime  burning"  is  not 
a  correct  one.  The  change  which  takes  place  during  the 
making  of  quick-lime  is  decomposition,  while  burning,  is 
combination  with  oxygen.  The  term,  however,  is  in  general 
use  and  is  unobjectionable,  provided  that  it  is  looked  upon 
merely  as  a  technical  term  for  a  commercial  process  with  no 
chemical  significance  attached  to  it. 

Calcium  carbonate  yields,  on  heating,  quick-lime  and  a  gas. 
From  the  quick-lime,  a  metal  may  be  extracted.  This  metal 
is  hard,  of  a  yellowish-white  colour,  tarnishes  rapidly  when 
exposed  to  the  air,  and  decomposes  water  at  ordinary  tem- 
peratures. It  is  known  as  calcium.  When  calcium  is  heated 
in  oxygen,  it  burns,  and  combines  with  the  oxygen  forming 
calcium  oxide,  and  this  compound  is  in  every  respect  identical 
with  quick-lime. 

From  the  gas  a  black  solid  can  be  extracted  by  passing  it 
over  heated  magnesium.  This  black  solid  is  known  as  carbon. 
When  carbon  is  burnt  in  oxygen  it  yields  carbon  dioxide  ;  this 
is  in  every  respect  identical  with  the  gas  given  off  during  lime 
burning. 

We  are  now  able  to  state  the  nature  of  the  change  more 
definitely  :  — 

Chalk          ^ 

AT    ui          I  w^en  neated  yields  calcium  oxide  and  carbon 

Limestone/      dioxide^ 
or  in  the  form  of  a  chemical  equation  — 


It  will  be  noticed  that  instead  of  using  the  customary 
sign  ->  in  this  equation,  we  have  used  one  with  an  arrow  head 
pointing  each  way.  This  is  to  signify  that  the  reaction  may 
take  place  in  either  direction,  i.e.  it  is  reversible.  It  means  that 
not  only  will  calcium  carbonate  decompose  into  quick-lime 
and  carbon  dioxide,  but  also  that  quick-lime  will  combine  with 
carbon  dioxide  to  form  calcium  carbonate.1  In  which  direction 

1  This  will  be  recognised  as  the  direct  union  of  an  acidic  with  a  basic 
oxide  to  form  a  salt, 

F 


66     A  FOUNDATION   COURSE   IN  CHEMISTRY 

the  reaction  will  proceed  depends  upon  the  temperature  and 
pressure. 

The  decomposition  of  calcium  carbonate  is  imperceptible 
until  a  temperature  of  about  500°  C.  is  reached.  Below  this 
temperature  the  only  reaction  noticeable  would  be  the  com- 
bination of  quick-lime  with  carbon  dioxide.  Even  at  tempera- 
tures above  500  C.,  if  the  calcium  carbonate  were  heated  in  a 
closed  vessel,  so  that  the  gas  was  not  able  to  escape,  there 
would  exist,  for  any  given  temperature,  a  condition  of  equilibrium 
in  which  decomposition  and  recombination  would  just  balance 
one  another,  and  the  reaction  would  never  be  completed.  .  It 
is  necessary  therefore  to  remove  the  carbon  dioxide  as  it  is 
formed. 

Lime.  —  One  of  the  chief  uses  of  quick-lime  is  for  the  making 
of  mortar.  The  lime  is  first  slaked  (p.  4)  — 


H2O-*Ca(OH)2 

The  slaked  lime  is  mixed  with  sand  and  water  to  make  a 
paste,  and  in  this  condition  is  used  for  building  purposes. 
Mortar,  however,  does  not  stick  bricks  together  as  gum  or 
glue  might,  although  mere  drying  may  be  considered  the  first 
stage  in  the  hardening  process.  The  actual  setting  depends 
upon  the  absorption  of  carbon  dioxide  from  the  air  and  the 
formation  of  calcium  carbonate  l  — 

Ca(OH)2  +  CO2  ->  CaC03  4-  H2O 

The  calcium  carbonate  thus  formed  acts  as  a  hard  cement 
binding  the  sand  grains  together. 

Another  action  is  said  to  take  place  slowly  under 
ordinary  conditions.  White  sand  is  a  compound  of  the 
element  silicon  (p.  106)  with  oxygen  (Si02).  It  is  an  acidic 
oxide,  and  may  possibly  combine  with  the  lime,  forming 
calcium  silicate.  The  formation  of  this  compound  would 
give  additional  •  hardness  to  the  mortar,  but  the  action  —  if.it 
occurs  at  all  —  is  extremely  slow. 

The  combination  of  lime   with   silica   takes  place  much 

1  This  action  must  of  necessity  commence  on  the  outside  of  the  mortar 
and  proceed  inwards. 


LIMESTONE  67 

more  rapidly  on  moderate  heating,  a  fact  which  is  utilised 
in  the  manufacture  of  the  so-called  lime-silica  bricks.  Here, 
the  two  substances  are  intimately  mixed  together,  moulded 
into  the  required  shape  and  treated  with  super-heated  steam 
under  pressure. 

Cement  is  another  important  material  of  which  lime  is  an 
essential  constituent.  Portland  cement  is  made  by  mixing 
lime  and  clay  in  proper  proportions.  The  mixture  is  heated 
strongly  until  it  just  begins  to  melt  (or  rather  to  vitrify  or 
become  glassy).  The  resulting  "clinker"  is  ground  to  fine 
powder;  this  is  the  "cement."  It  has  the  power  of  setting 
hard  when  in  contact  with  water,  and  unlike  mortar  does  not 
need  exposure  to  the  air. 

The  most  important  salts  of  calcium  are  the  phosphate 
(p.  97),  chloride,  CaCl2,  sulphate,  CaS04,  and  silicate  (p.  in). 

The  chloride  can  be  obtained  by  dissolving  calcium 
carbonate  or  hydroxide  in  hydrochloric  acid.  It  is  a  white 
solid  substance  which,  when  freed  from  water  of  crystallisation, 
is  largely  used  as  a  drying  agent.  It  takes  up  water  readily, 
and  quickly  becomes  damp  or  even  liquid  on  exposure  to  air 
through  absorption  of  atmospheric  moisture.  It  is  used  for 
drying  gases,  and  for  removing  water  from  many  liquids.1 

Calcium  Sulphate  occurs  fairly  plentifully  in  nature  as 
gypsum  or  alabaster  (CaSCU .  2H2O). 

It  can  also  be  prepared  by  mixing  strong  solutions  of  a 
soluble  sulphate  and  calcium  chloride — 

CaCl2  +  Na2SO4->  CaSO4  +  2NaCl 

Gypsum  is  largely  used  for  the  manufacture  of  plaster  of 
Paris.  When  it  is  heated  to  a  temperature  of  125°  C.  it  loses 
most  of  its  water  of  crystallisation  and  is  converted  into  a 
white  amorphous  powder.2  This  is  plaster  of  Paris.  Its 
utility  for  the  making  of  plaster  casts  depends  upon  its 

1  CaCl4  cannot  be  used  for  drying  alcohol.     It   combines   with   this 
liquid  as  it  does  with  water,  forming  a  crystalline  compound  in  which  the 
alcohol  takes  the  place  of  water  of  crystallisation.     Alcohol  must  be  dried 
with  quick-lime  (p.  148). 

2  This  is  probably  a  mixture  of  CaSO4.2H2O,  with  (CaSO4)2H80  and 
f.he  anhydrous  salt,  CaSO4. 


68     A  FOUNDATION    COURSE   IN    CHEMISTRY 

property  of  hardening  when  mixed  with  water.  This  harden- 
ing is  due  to  recombination  with  water  and  the  consequent 
formation  of  the  crystalline  substance  CaSO42H2O.  The 
crystals  formed  are,  however,  so  small  that  the  whole  mass 
appears  to  the  eye  non-crystalline  and  dead-white. 

When  gypsum  is  heated  too  strongly  it  loses  all  its  water 
of  crystallisation,  and  is  said  to  be  "dead-burnt."  In  this 
condition  it  is  useless  for  plaster,  as  it  will  no  longer  harden 
quickly  on  the  addition  of  water. 

Calcium  Carbide.  —  This  compound  is  formed  by  the  action 
of  carbon  on  quick-lime  at  a  very  high  temperature  — 


It  is  used  in  the  preparation  of  acetylene  gas  for  illumination, 
etc.  (see  also  p.  158). 

Carbon  Dioxide.  —  When  chalk  or  any  other  form  of  calcium 
carbonate  is  treated  with  an  acid,  effervescence  takes  place. 


FIG.  10. 

Effervescence  is  always  due  to  the  giving  off  of  gas,  and  the 
gas  in  this  case  is  carbon  dioxide.  The  same  gas  is  evolved 
when  calcium  carbonate  is  heated  strongly,  also  when  carbon 
is  burnt  in  oxygen — 

CaCO3  +  2HC1  ->  CaCl2  +  H2O  +  CO2 

The  gas  may  be  collected  by  downward  displacement. 
The  apparatus  generally  employed  is  shown  in  Fig.  10.  Into 


LIMESTONE  69 

the  flask  fragments  of  marble  are  placed,  and  dilute  hydro- 
chloric acid  added  by  means  of  the  funnel.  The  escaping  gas 
is  passed  through  water  contained  in  the  wash-bottle  to  remove 
all  traces  of  hydrochloric  acid,  and  then  is  collected  in  the 
gas-jar  by  downward  displacement.  To  tell  when  the  jar  is 
full  of  the  gas,  apply  a  lighted  taper  to  its  mouth;  the  gas 
will  immediately  extinguish  the  taper. 

Carbon  dioxide  is  a  colourless,  odourless,  tasteless  gas ;  it 
is  22  times  as  dense  as  hydrogen  (p.  34),  that  is,  about  ij 
times  as  heavy  as  air.  It  is  slightly  soluble  in  water,1  and  the 
solution  is  feebly  acid  to  litmus.  This  is  doubtless  due  to  the 
formation  of  the  unstable  carbonic  acid  H2CO3,  a  substance 
which  has  never  been  prepared  pure  (p.  163). 

The  heaviness  of  carbon  dioxide  can  be  shown,  by  pouring 
it  downwards  from  one  jar  to  another,  by  filling  soap  bubbles 
with  the  gas  (these  rapidly  descend),  or  by  filling  with  it  a 
beaker  placed  on  the  scale  pan  of  a  balance.  One  litre  of 
carbon  dioxide  weighs  2 '17  grams.  If  carbon  dioxide  be 
passed  through  lime  water  a  white  precipitate  of  calcium 
carbonate  is  thrown  down — 

Ca(OH)2  +  CO2  ->  CaCOa  -f  H2O 

This  reaction  is  used  as  a  test  for  the  presence  of  the  gas. 

If  the  passage  of  the  gas  through  the  lime  water  is  pro- 
longed, the  precipitate  first  formed  gradually  dissolves  owing 
to  the  formation  of  a  soluble  calcium  hydrogen  carbonate — 

CaCO3  +  CO2  -f  H20  ^  CaH2(CO3)2 

It  is  owing  to  this  action  that  limestone  and  chalk  dissolve  in 
river  '  and  spring  water.  These  invariably  contain  carbon 
dioxide — sometimes  in  considerable  quantities.  Water  thus 
rendered  impure  reacts  with  soap  (p.  165)  and  prevents  the 
formation  of  a  lather.  It  is  said  to  be  hard. 

1  At  760  mm.  pressure  and  15°  C.  water  dissolves  its  own  volume  of 
carbon  dioxide.  A  solution  made  under  a  pressure  of  about  3  atmospheres 
is  known  as  "soda  water."  The  relation  of  the  solubility  of  a  gas  to 
pressure  is  given  in  the  following  statement  generally  known  as  Henry's 
Law.  "The  concentration  of  a  saturated  solution  of  a  gas  is  proportional 
to  the  pressure  at  which  the  gas  is  supplied." 


70     A  FOUNDATION   COURSE   IN  CHEMISTRY 

The  "  hardness  "  thus  produced  may  be  reduced  in  several 
ways  :  — 

(1)  By  boiling.      The   equation   given   above   shows   the 
action  of  carbon  dioxide  and  water  upon  calcium  carbonate  as 
reversible.     It  is  reversed  if  the  water  is  heated,  for  then  the 
calcium  hydrogen  carbonate  is  decomposed  into  carbon  dioxide, 
water,  and  calcium  carbonate.     It  is  this  redeposited  calcium 
carbonate,  which  forms  the  "  fur  "  or  incrustation  in  boilers, 
and  the  thick  white  coating   often  found   on   the   insides  of 
kettles. 

(2)  By   adding   more   lime.      This  is   known   as   Clark's 
softening  process.     If  slaked  lime  or  lime  water  be  added  to 
water  containing  calcium  carbonate  in  solution,  the  added  lime 
combines  with  the  excess  of  carbon  dioxide.     It  is  therefore 
precipitated  together  with  the  calcium  carbonate  previously  in 
solution  — 


CaH2(CO3)2  +  Ca(OH),->  2CaC03  +  2H2O 
(3)  By  addition  of  ammonium  chloride  (sal   ammoniac). 
CaH2(CO3)2  +  2NH4C1  ->  CaG2 


Water  treated  in  this  way  could  not  be  used  for  domestic 
purposes.  It  is  not  actually  rendered  soft,  but  the  calcium  is 
all  converted  into  chloride,  and  this  salt  —  being  very  soluble 
—  does  not  form  a  "  fur  "  in  steam  boilers.1 

Because  hardness  produced  by  calcium  carbonate  is 
dispelled  by  boiling,  it  is  said  to  be  "  temporary."  Magnesium 
carbonate  dissolves  under  exactly  the  same  conditions  and 
affects  the  water  in  precisely  the  same  manner. 

1  Other  methods  of  softening  water  for  technical  purposes  are  employed, 
among  which  the  following  should  be  noted  :  — 

Certain  double  silicates  called  zeolites  —  which  contain  aluminium  and 
alkali  bases  and,  generally,  calcium  also  —  possess  the  property  of  exchang- 
ing the  alkali  for  the  calcium  or  magnesium  present  in  hard  water,  and 
are  therefore  used  to  soften  it.  When  the  alkali  is  entirely  replaced  by 
calcium  or  magnesium,  the  softening  power  of  the  zeolite  is  exhausted; 
it  is  said,  however,  that  it  can  be  regenerated  by  treatment  with  sodium 
chloride.  An  artificial  zeolite  is  sold  under  the  name  of  "Permutite" 
for  water  softening.  Certain  colloids,  such  as  tannin,  which  keep  cakium 
carbonate  in  suspension,  are  sometimes  used  to  prevent  the  formation  of 
boiler  fur. 


LIMESTONE  71 

Water  may  also  be  rendered  hard  by  the  presence  of  other 
compounds  in  solution,  but  in  these  cases  boiling  does  not 
soften  it;  such  hardness  is  said  to  be  permanent.  Calcium 
sulphate  is  the  most  common  cause  of  permanent  hardness. 
Water  containing  this  material  may  be  softened  by  the  addition 
of  sodium  carbonate  (washing  soda),  which  precipitates  the 
calcium  as  carbonate. 

CaSO4  +  Na2COa  =  CaCO3  +  Na2SO4. 

Among  other  substances  which  may  produce  permanent 
hardness  would  be  common  salt  (in  a  solution  of  which  soap 
does  not  dissolve)  and  mineral  acids  ;  the  latter  decompose  the 
soap. 

Carbon  dioxide  can  be  liquefied  at  *o°  C.  under  a  pressure 
of  35-4  atmospheres,  and  at  ordinary  atmospheric  pressure  the 
liquid  produced  boils  at  a  temperature  of  -  79°  C.  An 
important  point  in  regard  to  the  liquefaction  of  gases  may 
be  illustrated  by  reference  to  carbon  dioxide. 

As  a  rule,  gases  may  be  liquefied  by  lowering  the  tempera- 
ture, or  by  increasing  the  pressure,  more  often  by  both  means 
employed  at  the  same  time.  As  the  pressure  is  increased,  it 
becomes  less  necessary  to  reduce  the  temperature  of  the  gas. 
For  every  gas,  however,  there  is  a  certain  temperature  below 
which  it  must  be  cooled,  or  no  pressure,  however  great,  will 
liquefy  it.  This  is  known  as  the  critical  temperature,  and 
there  is  also  a  certain  minimum  pressure,  which  must  be  applied 
to  the  gas,  so  that  any  slight  lowering  of  the  temperature  of  the 
gas  below  the  critical  temperature  will  cause  liquefaction  to 
commence.  This  is  known  as  the  critical  pressure.  For  carbon 
dioxide  the  critical  temperature  and  pressure  are  31°  C.  and 
7  2 '5  atmospheres.  That  is,  'if  we  had  carbon  dioxide  in  a 
vessel  at  a  pressure  of  72-5  atmospheres  and  31°  C.,  then  any 
slight  lowering  in  temperature  would  produce  liquefaction  even 
if  the  pressure  remained  the  same ;  and  any  slight  increase  in 
pressure  would  also  cause  liquefaction  even  if  the  temperature 
remained  constant.  Any  slight  rise  in  temperature  would 
make  liquefaction  impossible. 

Carbon   dioxide   as   an    article   of   commerce   is  sold  in 


72     A  FOUNDATION   COURSE   IN  CHEMISTRY 

wrought-iron  cylinders  under  a  pressure  of  60  to  70  atmospheres, 
and  as  the  temperature  of  the  air  is  usually  considerably  below 
31°  C.,  the  carbon  dioxide  in  the  cylinder  is  generally  liquid, 
and  can  be  obtained  in  this  state  on  opening  the  tap  with 
which  the  cylinder  is  fitted.  If  the  emerging  jet  of  liquid  be 
beaten  into  fine  spray,  it  is  cooled  so  much  by  its  own  rapid 
evaporation,  that  it  freezes,  and  takes  the  form  of  a  white  snow, 
which  evaporates  slowly  and  without  melting.  Solid  carbon 
dioxide  mixed  with  either  forms  a  powerful  freezing  mixture. 

Carbon  dioxide  will  not  burn.  The  metals  sodium, 
potassium,  and  magnesium  will  burn  in  it,  combining  with  the 
oxygen  and  liberating  carbon ;  but  it  immediately  extinguishes 
the  flames  of  ordinary  combustibles.  Similarly  it  will  not 
support  respiration ;  for  this,  free  oxygen  is  necessary.  It  is 
not,  however,  considered  poisonous,  as  it  is  possible  to  breathe 
air  containing  5  per  cent,  of  the  gas  without  great  incon- 
venience. As  much  as  6  to  8  per  cent,  must  be  present 
before  any  signs  of  poisonous  action  appear,  and  it  is  said 
that  25  per  cent,  is  needed  to  cause  actual  danger  to  life. 

The  "  stuffiness  "  of  rooms  in  which  people  are  congregated 
is  due  not  so  much  to  the  accumulation  of  carbon  dioxide  as  to 
high  temperature,  the  presence  of  excess  of  water  vapour, 
and  of  organic  material  given  out  with  respired  air.1 

Carbon  dioxide  is  sometimes  referred  to  as  carbonic  acid. 
This  is  not  accurate ;  the  name  should  be  applied  only  to  the 
compound  H2CO3,  the  acid  of  which  CO2  is  the  anhydride. 
Although  this  acid  is  not  known  in  a  free  state  many  of  its 
salts,  known  as  carbonates,  are  familiar  to  us.  The  more 
important  will  be  described  under  their  respective  metals. 

1  Expired  air  after  removal  of  water  vapour  will  generally  contain 
CO2,  3^-4  per  cent.  ;  oxygen,  17-16^  per  cent. ;  nitrogen,  79^  per  cent. 


CHAPTER   IX 

COMMON    SALT 

Occurrence. — Common  salt  is  a  white  crystalline  solid.  It 
exists  in  solution  in  sea  water  to  the  extent  of  3*5  per  cent., 
and  in  some  countries  is  obtained  from  this  source  by  evapora- 
tion. In  many  places,  however,  it  occurs  in  large  mineral 
deposits.  In  England,  the  chief  districts  are  Worcestershire, 
Cheshire,  and  North  Staffordshire,  and  in  these  localities  it  is 
generally  obtained  by  allowing  water  to  enter  the  salt  deposit. 
The  saturated  brine  is  brought  to  the  surface  by  means  of 
pumps,  evaporated,  and  the  solid  salt  which  is  left  is  purified 
by  recrystallisation.  Often,  however,  it  is  mined,  and  the  solid 
blocks  of  salt  so  obtained  are  known  as  rock  salt. 

Common  salt  is  a  most  important  mineral,  not  only  because 
of  the  uses  to  which  it  can  itself  be  put,  but  also  because 
it  is  the  chief  source  of  the  compounds  of  sodium  and  of 
chlorine.  Many  of  these  compounds  are  of  great  value  in  the 
industries  and  in  medicine.  An  immense  industry  has  there- 
fore sprung  up  in  connection  with  common  salt. 

Properties. — The  appearance  and  taste  of  salt  are  familiar. 
Its  solubility  in  water  is  shown  in  the  diagram  (p.  27).  When 
pure,  it  is  neutral  to  litmus,  and  remains  dry  on  exposure  to 
the  air  ;  any  deliquescence  is  due  to  the  presence  of  impurities, 
chiefly  magnesium  chloride.  It  is  used  by  agriculturists  as  a 
condiment  for  cattle  foods,  and  is  sometimes  applied  to  the 
land,  but  probably  it  has  no  direct  manurial  value.  Its  use 
for  domestic  purposes  is  due  almost  entirely  to  its  value  as  a 
preservative  and  as  a  condiment. 

Spirit  of  Salt.— When  common  salt  is  treated  with  oil  of 
vitriol  a  colourless  gas  is  given  off  which  has  a  powerful  irritating 


74    A  FOUNDATION   COURSE   IN   CHEMISTRY 

odour.  It  fumes  strongly  in  the  air,  extinguishes  a  burning  taper, 
and  is  extremely  soluble  in  water.1  From  this  solution  it  is  not 
possible  to  drive  off  all  the  gas  by  heating.  When  it  is  boiled 
a  considerable  amount  of  the  gas  is  expelled,  but  a  mixture 
boiling  at  110°  C.  and  containing  20^2  per  cent,  of  hydrochloric 
acid 2  remains.  In  old  times,  when  gases  or  vapours  were  given 
off  they  were  often  referred  to  as  "  spirits,"  and  hydrochloric 
acid  was  known  as  "  spirit  of  salt,"  because  it  was  prepared 
from  salt.  The  name  is  still  occasionally  applied  to  it. 

The  solution  of  the  gas  in  water  is  strongly  acid.  The 
acidic  properties  were  among  the  first  properties  of  the  gas 
which  were  recognised,  and  it  consequently  received  the  name 
"  muriatic  acid,"  8  i.e.  the  acid  obtained  from  brine. 

Chlorine. — When  a  concentrated  solution  of  hydrochloric 
acid  is  treated  with  oxidising  agents,  another  gas  is  evolved, 
which  owing  to  its  method  of  preparation  was  originally  called 
oxy-muriatic  acid — it  was  thought  to  be  a  compound  of  muriatic 
acid  and  oxygen.  It  is  now  known  that  this  gas  is  an  element, 
and  because  of  its  yellow-green  colour,  the  name  chlorine 4  has 
been  given  to  it. 

Chlorine  has  a  powerful  irritating  odour  resembling  that  of 
chloride  of  lime  but  much  stronger.  It  cannot  be  breathed 
as  it  attacks  the  mucous  membrane  of  the  throat  and  nose. 
It  is  chemically  a  very  active  element ;  phosphorus  and  anti- 
mony take  fire  in  and  combine  with  it,  forming  chlorides.5  If 
the  gas  is  mixed  with  hydrogen  and  exposed  to  the  action  of 
sunlight  or  the  light  from  burning  magnesium,  the  hydrogen 
and  chlorine  combine  with  explosion.  Diffused  daylight  also 
causes  the  action  to  take  place,  but  more  slowly. 

This  action  is  one  of  great  importance,  for  the  product 

1  At  N.T.P.  one  volume  of  water  dissolves  525*2  volumes  of  the  gas  and 
then  contains  45  per  cent,  by  weight. 

2  If  a  dilute  solution  is  boiled,  water  first  comes  off,  and  the  tempera- 
ture gradually  rises  until  it  reaches  no°C.  when  the  same  2O'2  per  cent, 
solution  distils. 

The  fuming  of  HC1  in  the  air  is  due  to  the  great  solubility  of  the  gas 
in  water.  It  dissolves  in  the  atmospheric  moisture  and  the  solution  formed 
condenses  more  readily  that  the  moisture  itself. 

8  Latin,  muria,  brine. 

4  Gk.  x\up6s,  yellow  green. 

5  Instances  of  combustion  without  oxygen. 


COMMON   SALT  75 

is  the  gas  we  have  hitherto  called  spirit  of  salt  or  muriatic 
acid.  It  is  obviously  a  compound  of  hydrogen  and  chlorine, 
and  because  of  its  acidic  properties  it  is  known  as  hydrochloric 
acid.1  The  combination  of  hydrogen  and  chlorine  moreover 
helps  us  to  find  a  formula  for  hydrochloric  acid. 

When  equal  volumes  of  the  gases  are  mixed  and  com- 
bination takes  place,  the  gas  which  is  formed  has  exactly 
the  same  volume  as  the  original  mixture?  and  there  is  none 
of  either  gas  left  over,  i.e.  if  10  c.c.  of  hydrogen  were  mixed 
with  10  c.c.  of  chlorine  they  would  combine  and  form  20  c.c. 
of  hydrochloric  acid  gas. 

Avogadro's  hypothesis. — "  Under  the  same  conditions  of 
temperature  and  pressure,  equal  volumes  of  gases  contain  an 
equal  number  of  molecules."  This  statement,  known  from 
the  name  of  its  author  as  Avogadro's  hypothesis,  although  it 
scarcely  admits  of  rigid  proof,  has  been  found  to  withstand 
all  criticism.  Assuming  it  to  be  true,  then  in  our  experiment 
of  the  combination  of  hydrogen  and  chlorine,  the  number  of 
molecules  after  the  experiment  is  the  same  as  it  was  before. 
But  whereas  before  the  combination  half  of  the  molecules 
were  chlorine  and  half  were  hydrogen,  after  the  combination 
they  are  all  molecules  of  hydrochloric  acid.  Suppose  we  have 
one  molecule  of  hydrogen  and  one  molecule  of  chlorine  —  that 
is,  two  molecules  altogether — after  combination  we  still  have 
two  molecules,  but  they  are  both  molecules  of  hydrochloric 
acid.  The  only  way  in  which  this  can  be  brought  about  is 
by  dividing  each  chlorine  and  hydrogen  molecule  into  two 
equal  parts,  and  causing  each  half  molecule  of  the  one  to 
combine  with  a  half  molecule  of  the  other.  The  diagram 
may  make  this  clearer. 

One  molecule  of  {  ( . ,  WlfflMfflA     \  °ne  ™?le.cule  °f 

hydrogen.       1   [  W///M/M     >          chl°rlne> 


Two  molecules  of  hydrochloric  acid. 

1  Also  as  hydrogen  chloride. 

-  i.e.  If  temperature  and  pressure  are  the  same  as  they  were  before  the 
experiment. 


76     A   FOUNDATION   COURSE    IN  CHEMISTRY 

By  no  method  hitherto  discovered  has  it  been  found 
possible  to  divide  either  the  chlorine  or  hydrogen  molecule 
into  more  than  two  parts,  and  therefore  both  of  these  elementary 
molecules  are  said  to  consist  of  two  atoms,  and  the  molecule 
of  hydrochloric  acid  must  consist  of  one  atom  of  hydrogen 
and  one  of  chlorine.1  Hydrochloric  acid  is,  therefore,  repre- 
sented by  the  formula  HC1. 

Properties  of  Chlorine. — Chlorine  is  a  heavy  gas  (density 
35-46  compared  with  hydrogen),  and  is  therefore  generally  col- 
lected by  downward  displacement.  The  following  experiments 
can  be  performed  to  demonstrate  its  chemical  properties  : — 

(a)  Yellow  phosphorus  burns  in  chlorine  with  a  pale  flame 

forming  chlorides  of  phosphorus,  PC13  and  PC15. 

Antimony  in  the  form  of  fine  powder  also  burns  in 
chlorine,  forming  SbCl3. 

(b)  Sodium  combines   with   the  gas   and    forms   a   white 

solid  which  taste  and  other  properties  show   to   be 
common  salt. 

(c)  A  lighted  taper  will  burn  in  chlorine  gas,  but  with  a 

dull  red  and  very  smoky  flame. 

(d)  Chlorine  acts  on  turpentine  with  great  energy,  generally 
causing  it  to  take  fire  and  deposit  a  large  quantity  of 
soot. 

(e)  Coloured   materials,  such  as  turkey-red,  litmus  paper, 

paper  with  writing  ink,  when  moistened  with  water  are 

bleached  by  chlorine,  but  black  printing  ink,  being  a 

preparation  of  carbon,  is  not  affected. 

These  three  actions  depend  upon  the  affinity  of  chlorine 

for  hydrogen.     Turpentine  and  the  wax  of  the  taper  are  both 

compounds  of  carbon  and  hydrogen,  and  in  each  case  the 

chlorine  combines  with   the   hydrogen   forming  hydrochloric 

acid  and  liberating  the  carbon  which  appears  as  smoke  or  soot. 

The  bleaching  action  of  chlorine  (Exp.  (c))  is  due  to  the 

same  cause ;  chlorine  does  not  bleach  except  in  the  presence 

1  The  formula  cannot  be  any  multiple  of  this,  say  H,,C1,,,  for  then  the 
volume  of  the  combined  gases  would  be  -  of  what  it  was  when  they  were 
merely  mixed. 


COMMON   SALT  77 

of  moisture.  It  combines  with  the  hydrogen  of  the  water 
forming  a  small  quantity  of  hypochlorous  acid  and  hydrochloric 
acid.  The  reaction  is  reversible — 

H20  +  C12^HC10  +  HC1 

Hypochlorous  acid1  is  the  immediate  bleaching  agent.  It 
readily  parts  with  its  oxygen ;  this  oxidises  the  colouring 
matter  which  is  thereby  destroyed.2 

The  form  in  which  chlorine  is  generally  used  for  bleaching 
is  that  of  "  chloride  of  lime "  (bleaching  powder).  This 
substance  is  prepared  by  passing  chlorine  over  slaked  lime  until 
no  more  of  the  gas  is  absorbed.  The  product  is  a  soft,  whitish 
powder,  having  an  odour  similar  to  that  of  chlorine.  It 
contains  Ca(OH)2  and  another  substance  generally  represented 
by  the  formula  CaOCl2,  which  as  regards  the  quantities  of  the 
elements  present  is  equivalent  to  a  mixture  of  (calcium  chloride) 
CaCl2  and  (calcium  hypochlorite)  Ca(OCl)2,3  and  in  a  solution 
in  water  these  compounds  are  present.  It  is  clear,  however, 
that  bleaching  powder  cannot  be  a  mixture  of  these.  If  it 
were,  the  large  amount  of  calcium  chloride  present  would  make 
it  very  deliquescent,  which  it  is  not.  It  bleaches  by  means  of 
the  hypochlorite  formed  with  water. 

Only  coarse  materials  can  with  safety  be  bleached  with 
chlorine  or  bleaching  powder.  More  delicate  fabrics,  such  as 
linen,  silk,  etc.,  would  be  seriously  injured. 

The  use  of  chlorine  and  chloride  of  lime  is  not  confined  to 
bleaching;  the  substances  are  used  as  powerful  deodorizers 
and  disinfectants,  this  action  being  also  due  to  oxidation  in 
the  presence  of  moisture. 

Chlorine  is  moderately  soluble  in  water ;  the  solution  has  a 
faintly  yellow  colour  and  is  known  as  chlorine  water.  It  is 
not  very  stable.  Traces  of  hypochlorous  acid  and  hydrochloric 
acid  are  formed,  and  under  the  influence  of  sunlight  the 

1  Four  oxyacids  of  chlorine  are  known  :   HC1O,  hypochlorous  acid ; 
HC1O2,  chlorous  acid  j  HC1O3,  chloric  acid  ;  HC1O4  perchloric  acid.     It  will 
be  seen  the  nomenclature  for  these  acids  is  similar  to  that  we  have  used 
for  oxides  and  other  compounds.     The  prefix  "hypo  "  is  from  the  Greek 
{/wo,  under,  and  is  applied  to  the  acid  containing  less  oxygen  than  the 
"  ous  "  compound.     This  nomenclature  is  regularly  employed. 

2  Note  that  bleaching  by  chlorine  is  a  process  of  oxidation, 

3  CaCl2  +  Ca(OCl2)  =  CasO2Cl4  =  2CaOCl8. 


78     A  FOUNDATION    COURSE   IN   CHEMISTRY 

hypochlorous  acid  loses  oxygen,  forming  hydrochloric  acid. 
Unless  therefore  chlorine  water  is  kept  in  the  dark  it  gradually 
changes  into  hydrochloric  acid  with  the  liberation  of  oxygen  gas. 

Having  dealt  with  both  the  elements  present  in  hydrochloric 
acid,  and  established  its  formula,  it  is  now  possible  to  study 
the  properties  of  the  acid  itself  with  greater  accuracy. 

As  previously  stated,  it  is  prepared  by  the  action  of  sulphuric 
acid  upon  common  salt  — 

NaCl  +  H2SO4  ->  NaHSO4  +  HC1 

At  a  high  temperature  a  larger  quantity  of  common  salt 
may  be  decomposed  by  the  same  amount  of  acid  — 
2NaCl  +  H2SO4->  Na2SO4  +  2HC1  1 

The  hydrochloric  acid  must  be  collected  either  over 
mercury  or  by  downward  displacement  (its  density  compared 
with  air  is  1*23). 

Properties  of  Hydrochloric  Acid.—  (i)  It  can  be  neutralized 
by  bases,  when  it  forms  salts  and  liberates  water  — 
HC1  +  NaOH  ->  NaCl  +  H2O 


(2)  Certain  metals,  notably  zinc,  iron,  magnesium,  and 
aluminium,  dissolve  in  solutions  of  hydrochloric  acid,  liberating 
hydrogen  and  forming  chlorides,  which  can  be  obtained  by 
evaporation  of  the  solution  — 

Fe  +  2HC1   ->  FeCl2  +  H2 

Zn  +  2HCl->ZnCl2  +  H22 

Mg-f-2HCl->MgCl2  +  H23 

2A1 


1  Any  other  chloride  would  act  in  the  same  manner  —  in  fact,  the  libera- 
tion of  HC1  with  sulphuric  acid  is  used  as  a  test  for  chlorides. 

2  If  the  aqueous  solution  of  zinc  chloride  be  evaporated,  the  salt  is 
acted  upon  by  the  water  forming  a  basic  chloride,  Zn2OCl2.     ZnCl2  can  be 
obtained  by  evaporation  in  presence  of  excess  of  HC1. 

3  Magnesium  chloride  may  be  obtained  on  evaporation  as  a  deliquescent 
crystalline  solid,  MgCl2.6H2O.     When,  however,  this  substance  is  heated 
it  is  partly  decomposed,  some  magnesium  oxide  being  formed. 

4  If  the  solution  be  allowed  to  evaporate  spontaneously  A1C13.6H2O  is 
formed.     On  heating,  however,  it  is  completely  decomposed  — 

2A1C13  +  3H20  ->  A1203  +  6HC1 

Action  by  water  in  the  manner  of  these  three  examples  is  known  as 
hydrolysis, 


COMMON   SALT  79 

Hydrochloric  acid  may  be  liquefied  by  pressure  alone. 
The  anhydrous  liquid  shows  no  acid  properties,  and  will  not 
conduct  electricity,  thereby  differing  from  the  solution  in 
water. 

The  Halogens.  —  The  power  of  forming  an  acid  and  salts 
with  hydrogen  or  a  metal  only  is  not  confined  to  chlorine  but 
is  shared  by  a  group  of  closely  allied  elements,  bromine, 
iodine,  and  fluorine  (p.  112),  and  these,  with  chlorine,  because 
of  their  salt  forming  properties,  have  been  called  the  halogens.1 
The  acids  are  hydrobromic,  hydriodic,  and  hydrofluoric  acids, 
HBr,  HI,  H2F2,  and  the  salts  are  known  KBr,  KI,  KHF2,  KF, 
respectively  as  bromides,  chlorides,  and  iodides.  They  are 
monobasic  acids  with  the  exception  of  hydrofluoric  acid, 
which  is  dibasic,  as  is  shown  by  the  fact  that  it  forms  two 
salts  with  potassium. 

The  Oxidation  of  Hydrochloric  Acid.  —  This  leads,  as  already 
stated,  to  the  liberation  of  chlorine  — 


(1)  If  air  or  oxygen  is  mixed  with  hydrochloric  acid  gas 
but  little  action  takes  place  even  when  the  gases  are  strongly 
heated.     A  commercial  method  of  preparing  chlorine  by  the 
oxidation  of  HC1  with  free  oxygen  has,  however,  been  devised. 
It  is  known  as  Deacon's  process,  and  depends  for  its  effective- 
ness  upon  the   presence  of  a  catalytic2  agent;  in  this  case 
cupric  chloride,  or  sulphate.     Hydrogen  chloride  gas  mixed 
with  air  is  passed  over  bricks,  or  other  porous  material,  which 
have  been  soaked  in  a  solution  of  the  copper  salt,  dried,  and 
heated  strongly  while  the  gases  are  being  passed  over  them. 
Under  these  conditions  oxidation  of  the  hydrochloric   acid 
takes  place  and  a  considerable  amount  of  chlorine  is  produced. 

(2)  By  the  action  of  manganese  dioxide  — 

Mn08  -f  4HCl->MnCl2  +  2H2O  +  C12 

1  Gk.  oAs,  salt  ;  yevvdw,  I  produce. 

2  Gk.  Kara,  down  ;  \vffts,  a  loosening.    A  catalytic  agent  is  one  which 
assists  other  substances  to  react,   without  itself  undergoing  any  apparent 
change.     The  action  of  manganese  dioxide  and  iron  oxide  in  assisting  the 
liberation  of  oxygen  from   potassium   chlorate    is    another    instance    of 
catalysis  (p.  19). 


8o     A  FOUNDATION   COURSE    IN    CHEMISTRY 

(3)  By  the  action  of  red  lead  — 

2Pb304  +  i6HCl  ~>  6PbCl2  +  8H20  +  2C12 

(4)  By  the  action  of  potassium  bichromate  — 
K2Cr2O7  +  I4HC1  ->  2KC1  +  2CrCl3  +  ?H2O  +  30, 

(5)  By  the  action  of  potassium  permanganate  — 
2KMnO4  -}-  i6HCl->  2KC1  +  2MnCl2  +  8H2O  +  SC12 

All  these  oxidizing  agents  could  be  used  for  preparing 
chlorine  from  hydrochloric  acid,  and  in  fact,  with  the  exception 
of  red  lead,  are  often  used. 

(6)  By  the  action  of  nitric  acid. 

Neither  nitric  acid  nor  hydrochloric  acid  is  alone  capable 
of  acting  upon  such  metals  as  gold  or  platinum,  but  a  mixture 
of  the  two  acids  dissolve  them  both.  This  is  due  to  the  fact 
that  nitric  acid,  like  other  oxidising  agents,  liberates  chlorine 
from  hydrochloric  acid  — 

HNO3  +  3HC1-*  2H2O  +  NOC1  +  C12 

(nitrosyl 
chloride). 

It  is  the  free  chlorine  which  attacks  the  metal,  and  the 
chloride  is  formed  in  each  case.  Because  these  mixed  acids 
can  dissolve  gold,  called  in  early  times  a  "noble"  metal,  the 
name  Aqua  Regia  has  been  given  to  the  mixture. 

In  order  to  obtain  chlorine  from  a  chloride  it  is  not 
necessary  first  to  prepare  hydrochloric  acid  and  then  oxidise  it. 
If  a  mixture  of  the  chloride,  manganese  dioxide,  and  sulphuric 
acid  be  employed,  both  changes  take  place  simultaneously  — 

MnO2  +  2NaCl  +  2H2SO4->  MnSO4+  Na2SO4  +  C12  +  2H2O 

As  a  rule,  however,  chlorides  of  metals  are  stable  substances, 
but  certain  chlorides  such  as  those  of  gold  and  platinum 
decompose  on  heating,  leaving  the  metal  — 

>Pt  +  2C1 


unaffected  by  heating. 

Sodium.  —  This  is  the  other  element  present  in  common  salt. 
It  is  a  bright  whitish  metal  which  rapidly  tarnishes  in  moist 
air,  so  light  that  it  floats  on  water  and  soft  enough  to  be  cut 


COMMON   SALT  81 

with  a  knife.  It  decomposes  water  with  the  formation  of 
caustic  soda  (sodium  hydroxide) — 

2Na  4-  2HX)  ->  2NaOH  +  H.2, 

and  forms  a  salt  with  every  known  acid.  Practically  all  of  these 
salts  are  soluble  in  water. 

The  salts  of  sodium  are  largely  used  in  the  industries  and 
in  medicine.  The  following  are  the  more  important : — 

Sodium  Carbonate. — This  salt  is  sold  in  crystals  as 
"washing  soda"  or  soda  crystals.  There  are  two  important 
methods  in  use  for  its  manufacture. 

(a)  The  Le  Blanc  process. 

Common  salt  is  treated  in  a  special  furnace  with  sulphuric 
acid,  by  which  it  is  converted  into  sodium  sulphate  and 
hydrochloric  acid  is  set  free.  The  hydrochloric  acid  is  caused 
to  pass  up  tall  "scrubbing  towers"  down  which  water  is 
trickling,  so  that  it  is  completely  dissolved.  The  resulting 
solution  is  used  as  crude  hydrochloric  acid. 

The  sodium  sulphate  forms  a  white  mass,  which  is  technically 
known  as  salt  cake.  It  is  mixed  with  carbon  (powdered  coke) 
and  calcium  carbonate  and  heated  strongly — 

Na2SO4  +  2C  ->Na2S  +  2CO2 
Na2S  4-  CaCO3->  Na,CO3  +  CaS 

The  mixture,  which  is  black  through  excess  of  carbon  and 
therefore  known  as  black  ash,  is  lixiviated  with  water,  in 
which  calcium  sulphide  is  not  readily  soluble,  and  the  solu- 
tion of  sodium  carbonate  thus  obtained  is  evaporated.  The 
crystals  of  sodium  carbonate  which  separate  have  the  formula, 
Na2CO3.ioH2O.  These  crystals  are  very  efflorescent. 

(b)  The  Solvay  process. 

The  Le  Blanc  process  is  still  used  because  of  the  value  of  the 
bye  products,  sodium  sulphate  and  hydrochloric  acid,  but  a 
much  purer  carbonate  may  be  obtained  by  the  Solvay  or 
ammonia  soda  process.  In  this,  carbon  dioxide  is  passed 
through  a  solution  of  common  salt  saturated  with  ammonia. 
The  carbon  dioxide  reacts  with  the  ammonia  and  water  to 
form  ammonium  hydrogen  carbonate — 

NH.3  +  H,O  +  CO,->  NH4HCO3 

G 


82     A   FOUNDATION   COURSE    IN    CHEMISTRY 

This  compound  reacts  with  the  sodium  chloride,  forming 
sodium  hydrogen  carbonate — 

NH4HCO3  +  NaCl  ->  NaHCO3  +  NH4C1 

which  being  less  soluble  in  water  separates  and  is  collected. 
It  is  then  heated  strongly,  when  it  decomposes  and  leaves 
sodium  carbonate — 

2NaHCO3->Na2CO3  +  H2O 

The  compound  NaHCO3  may  also  be  prepared  by  passing 
carbon  dioxide  through  a  solution  of  sodium  carbonate — 

Na2CO3  +  H2O  -f  CO2^2NaHC03 

As  shown  above,  this  compound  is  decomposed  on  heating. 
It  is  sold  under  the  name  of  sodium  bicarbonate,  and  is  largely 
used  in  medicine  and  in  the  making  of  baking  powder. 

Sodiimi  sulphate.  This  salt  also  crystallises  from  water, 
solution  in  white  efflorescent  crystals  having  the  composition 
Na2SO4.ioH2O.  It  is  known  as  Glauber's  salt. 

Sodium  sulphite  occurs  as  white  efflorescent  crystals, 
Na2SO3.7H2O  (p.  87). 

Sodium  thiosulphate,  Na2S2O3.6HaO  (the  "hypo"  of  the 
photographer). 

Sodium  nitrate,  NaNO3,  Chili  saltpetre,  used  as  a  nitro- 
genous manure  (p.  132). 

Sodiiim  silicate,  Na2SiO3,  water  glass,  used  for  fireproofing 
wood  and  other  materials,  and  also  as  an  egg  preservative 
(p.  106). 

Caustic  soda,  sodium  hydroxide,  is  not  usually  made  by 
the  action  of  sodium  upon  water  but  by  the  interaction  of 
slaked  lime  upon  sodium  carbonate — 

Ca(OH)2  +  Na2C03->  2NaOH  +  CaCO;! 

The  calcium  carbonate  being  insoluble  separates  from  the 
mixture  and  the  clear  solution  of  sodium  hydroxide  is 
evaporated  to  dryness. 

Sodium  pyroborate,  Na2B4O7,  borax  (p.  114). 


CHAPTER   X 

SULPHUR 

Occurrence. — The  element  sulphur  is  very  widely  distributed 
in  nature.  It  occurs  both  free  and  in  combination.  Free,  it 
is  often  found  in  volcanic  districts,  where  its  exists  as  a  yellow 
crystalline  material.  For  a  long  time  the  world's  chief  supply 
was  derived  from  the  sulphur  mines  of  Etna.  Now,  however, 
large  quantities  are  obtained  from  the  United  States.  A  deposit 
of  native  sulphur  was  discovered  in  1865  in  the  State  of 
Louisiana,  but  the  difficulties  of  mining  it  were  not  overcome 
until  much  more  recently.  The  sulphur  is  now  obtained  by 
sending  down  water  heated  under  pressure  to  a  temperature  of 
385°  F.  (196°  C).  This  melts  the  sulphur,  which  is  brought 
to  the  surface  by  means  of  pumps. 

In  combination,  sulphur  occurs  both  as  sulphides  and 
sulphates,  the  former  often  providing  valuable  ores  of  the 
metals.  The  more  important  are  lead  sulphide  (Galena),  PbS, 
zinc  sulphide  (Blende),  ZnS,  mercuric  sulphide  (Cinnabar),  HgS, 
copper  pyrites,  CuFeSa.  Iron  pyrites,  FeS2,  another  sulphide, 
occurs  in  large  quantities.  It  is  chiefly  used  in  the  manu- 
facture of  sulphuric  acid. 

Calcium  sulphate  (p.  67)  is  the  only  sulphate  which  occurs 
in  nature  in  really  large  quantities.  Barium  sulphate  (BaSO4), 
known  as  barytes  or  heavy  spar,  is  also  of  somewhat  frequent 
occurrence,  and  is  largely  used  both  as  a  source  of  <the  com- 
pounds of  barium  and  also  as  a  constituent  of  many  white 
paints.  Potassium  sulphate  occurs  in  the  salt  deposits  of 
Stassfurt  in  Germany.  Sodium  sulphate  and  magnesium 
sulphate  are  frequently  found  in  the  waters  of  mineral  springs. 

Modifications. — Sulphur  as    an  article   of   commerce    is 


84    A   FOUNDATION    COURSE   IN   CHEMISTRY 

generally  supplied  cast  in  thick  sticks  or  rolls  and  known  as 
roll  sulphur,  also  as  a  fine  powder  known  as  flowers  of  sulphur, 
and  as  milk  of  sulphur.  Roll  sulphur  is  a  yellow,  brittle  solid. 
When  gently  heated  it  melts  at  120°  C.,1  forming  mobile  pale 
yellow  (amber-coloured)  liquid.  At  1 60°  C.  the  liquid  under- 
goes change  in  colour  and  consistency,  becoming  almost  black, 
and  so  viscous  that  it  cannot  be  poured  out  of  the  vessel.  At 
260°  C.,  without  changing  colour,  it  becomes  less  viscous,  and 
at  445°  it  boils,  giving  off  a  vapour  which  condenses  again 
to  a  pale  yellow  solid. 

If  melted  sulphur  be  cooled  slowly  it  assumes  a  crystalline 
form.  This  is  seen  when  the  thin  crust  which  forms  on  the 
surface  is  broken,  and  the  still  liquid  portion  of  the  sulphur  is 
poured  out.  The  crust  is  then  removed,  and  a  mass  of  trans- 
lucent crystals,  long  and  needle-like  in  form,  is  found  under- 
neath. This  is  the  prismatic  or  monoclinic  form  of  crystalline 
sulphur.  These  crystals  are,  however,  only  permanent  if  kept 
above  96°  C.  At  lower  temperatures  they  undergo  change, 
and  in  a  few  flays  lose  their  translucent  appearance  and  become 
pale  yellow  and  opaque.  Each  long  prismatic  crystal  is  changed 
into  a  mass  of  small  crystals  of  a  different  shape.  The  crystalline 
form  thus  obtained  is  that  which  is  permanent  at  ordinary 
temperatures.'2  It  may  be  prepared  more  conveniently  by 
crystallising  sulphur  from  solution  in  carbon  bisulphide.  If 
roll  sulphur  be  treated  with  this  liquid,  it  will  almost 
entirely  dissolve,  and  a  clear  yellow  solution  will  be  formed, 
which  on  evaporation  yields  octohedral3  crystals.  If,  instead 
of  being  allowed  to  cool  slowly,  boiling  sulphur  is  poured 
into  cold  water,  by  which  it  is  cooled  too  rapidly  to  allow 
crystals  to  be  formed,  it  becomes  converted  into  an  elastic 
modification  sometimes  known  as  "plastic  sulphur."4  It  is 
amorphous5  (i.e.  non-crystalline)  and  insoluble  in  carbon 

1  The  two  crystalline  forms  of  sulphur  have  different  melting  points, 
the  octohedral  form  melting  at  1 15°  C.  and  the  prismatic  at  120°  C.    Above 
96°  C.  the  octohedral  sulphur  is  converted  into  the  prismatic  variety. 

2  It  is  therefore  the  form  in  which  free  sulphur  occurs  in  nature. 

3  An  octohedron  is  a  solid  figure  having  eight  triangular  faces. 

4  This  transformation  does  not  seem  to  take  place  with  perfectly  pure 
sulphur. 

5  Gk.  juop<£^,  form  ;  d,  privative  particle. 


SULPHUR  85 

bisulphide.  After  a  few  days  this  form  also  becomes  opaque 
and  brittle,  and  is  then  found  to  have  largely  changed  into  the 
octohedral  variety,  but  a  considerable  proportion  remains  in  an 
amorphous  condition. 

Milk  of  sulphur  is  a  very  finely  divided  amorphous  form  of 
the  element,  thrown  down  from  aqueous  solutions  of  polysul- 
phides  or  thiosulphates  when  they  are  treated  with  acids.  It  can 
be  prepared  readily,  by  boiling  sulphur  with  milk  of  lime  or 
caustic  soda,  in  which  it  gradually  dissolves,  forming  a  yellow 
solution  which  contains  a  mixture  of  sulphides  and  thiosulphate 
of  calcium  or  sodium.  On  the  addition  of  an  acid — preferably 
hydrochloric — milk  of  sulphur  is  thrown  down  as  an  almost  white 
precipitate.  It  is  insoluble  in  carbon  bisulphide. 

"  Flowers  of  sulphur  "  is  the  name  given  to  the  condensed 
vapour  of  sulphur. 

From  the  foregoing  it  will  be  seen  that  pure  sulphur  may 
exist  in  several  different  forms,  a  property  which  is  shared  by 
certain  other  elements,  e.g.  oxygen,  phosphorus,  and  carbon 
(q.v.).  This  property  is  known  as  allotropy.1 

Oxides  and  Acids. — Sulphur  is  quite  insoluble  in  water, 
but  if  finely  powdered  sulphur  be  moistened  and  exposed  to 
the  air,  the  water  will,  in  a  short  time,  show  the  presence  of 
sulphuric  acid — 

28  +  2H2O  -f  3<D2->  2H2SO4 

When  sulphur  is  burned  in  a  known  volume  of  oxygen,  e.g. 
as  shown  in  Fig.  n,  the  resulting  gas  (sulphur  dioxide),  after 
being  allowed  to  cool  and  brought  to  the  original  pressure, 
occupies  exactly  the  same  volume  as  the  oxygen  did.  The 
number  of  molecules  is  therefore  unchanged,2  i.e.  for  every 
molecule  of  oxygen  used,  there  is  now  a  molecule  of  sulphur 
dioxide.  Each  molecule  of  sulphur  dioxide  must  therefore 
contain  one  molecule  of  oxygen.  But  the  molecule  of  oxygen 
contains  two  atoms,  therefore  each  molecule  of  sulphur  dioxide 
contains  two  atoms  of  oxygen.  This,  however,  does  not 
show  how  many  atoms  of  sulphur  there  are  in  the  molecule, 

1  Gk.  #\\os,  another  ;  r/xfa-oy,  manner,  form.     See  note  on  Allotropy 
at  the  end  of  this  chapter. 
-  Avogadro's  hypothesis. 


86     A   FOUNDATION    COURSE   IN    CHEMISTRY 


FIG.  ii, 


In  order  to  determine  this,  it  is  necessary  to  ascertain  the 

density  of  the  gas,  which  is  found  to  be  32  (i.e.  it  is  32  times  as 
heavy  as  an  equal  volume  of  hydrogen). 
But  the  density  of  a  gas  is  one-half  of  its 
molecular  weight,1  and,  therefore,  the  mole- 
cular weight  of  sulphur  dioxide  is  64.  The 
atomic  weight  of  sulphur  is  32,  that  of 
oxygen  16,  and,  therefore,  as  two  atoms  of 
oxygen  equal  32 ;  this  leaves  32  for  all  the 
sulphur  present,  which  is  exactly  the  weight 
of  an  atom  of  sulphur  in  terms  of  one  atom 
of  hydrogen.  There  is,  therefore,  one  atom  of 
sulphur  in  the  molecule  of  sulphur  dioxide, 
and  its  formula  is  SO.2. 

Burning  sulphur  in  oxygen  is  not  the 
only  method  of  preparing  sulphur  dioxide ; 
it  is  often  obtained  by  heating  concentrated 

sulphuric  acid  with  copper,  when  a  reaction  takes  place  which 

is  represented  by  the  equation — 

Cu  +  2H2SO4  ->  CuSO4  +  SO,  +  2H2O 

Other  metals,  such  as  silver  and  mercury,  act  in  the  same  way. 

A  similar  reaction  takes  place  when  sulphur  or  carbon  is  heated 

with  sulphuric  acid — 

S  +  2H2S04->3SO.,+ 2H2O 
C  +  2H2SO4  ->  CO2  +  2SO2  -f  2H2O 

Sulphur  dioxide  cannot  be  collected  over  water  as  it  is  soluble, 
so  the  method  of  downward  displacement  is  generally  em- 
ployed, as  in  the  case  of  chlorine.  It  extinguishes  a  lighted 
taper,  will  not  burn,  and  does  not  produce  any  precipitate  with 

1  This  is  true  for  all  gases,  for  it  simply  depends  upon  the  fact  that  the 
molecule  of  hydrogen  consists  of  two  atoms. 

Equal  volumes  of  gases  contain  equal  numbers  of  molecules  (temperature 
and  pressure  being  the  same),  therefore  the  density  of  gases  are  proportional 
to  their  molecular  weights.  We  compare  all  these  densities  with  hydrogen 
as  unity.  Now  the  molecular  weight  of  hydrogen  is  2,  and  if  the  molecular 
weight  of  a  gas  is  M,  the  densities  of  the  gas  and  of  hydrogen  are  in  the 

proportion  M  to  2,  that  is,  the  gas  is  —  times  as  heavy  as  hydrogen  ;  and  in 

general  the  density  of  a  gas  is  one -half  of  its  molecular  weight.  (See  note 
at  the  end  of  this  Chapter.) 


SULPHUR  87 

lime  water.  The  solution  in  water  is  acid  and  smells  strongly 
of  the  gas. 

Sulphur  dioxide  is,  therefore,  an  acidic  oxide ;  the  acid  is 
present  in  the  solution,  and  is  known  as  sulphurous  acid.1 

SO2  +  H2O  ->  H2S03 

Because  the  gas  forms  this  acid  with  water  it  is  often  referred 
to  as  sulphurous  anhydride.2 

Sulphurous  acid  is  a  dibasic  acid.  It  forms  two  salts  with 
soda,  the  normal  salt  occurring  in  crystals  of  the  formula 
Na2SO3.7H2O.  Sodium  hydrogen  sulphite,  NaHSO3,isa  white 
non-crystalline  powder.  All  sulphites  when  treated  with  dilute 
hydrochloric  or  sulphuric  acid  give  off  sulphur  dioxide — 

Na2S03  +  2HC1  ->  2NaCl  +  H2O  +  SO2 

Sulphurous  acid,  or  moist  sulphur  dioxide,  is  largely  used  for 
bleaching  such  material  as  wood,  straw,  wool,  and  silk.  The 
colouring  matter  often  forms  colourless  material  with  the  acid, 
or  may  be,  in  some  cases,  completely  destroyed.  Dilute  hydro- 
chloric acid  or  sulphuric  acid  will  sometimes  restore  the  colour. 
Sulphurous  acid  is  a  reducing  agent.  It  is  slowly 
oxidised  by  free  oxygen,  but  will  rapidly  withdraw  oxygen  from 
oxygen  compounds.  It  will  remove  oxygen  from  water  if  some- 
thing else  is  present  with  which  the  liberated  hydrogen  may 
combine.3  In  this  manner  it  decolorises  iodine  solution — 

H2SO3  4-  2!  +  H2O  ->  H2SO4  +  2HI 

Sulphur  dioxide  or  sulphurous  acid  may  readily  be  recognised 
by  its  odour  or  by,  its  reducing  action.  A  piece  of  paper 
coloured  yellow  with  a  solution  of  potassium  chromate  turns 
green  owing  to  the  formation  of  a  chromic  compound.  A 
still  more  delicate  test  is  provided  by  a  piece  of  paper  dipped 
in  a  solution  of  potassium  iodate  and  starch.  A  very  minute 
amount  of  sulphur  dioxide  will  cause  the  paper  to  turn  blue 

1  The  sulphur  dioxide  is  completely  driven  off  from  solution  by  boiling. 

2  The  term  "Anhydride"  is  often  applied  to  acidic  oxides  ;  it  means 
an  acid  minus  water. 

3  In  this  case  sulphurous  acid  would  appear  to   reduce  by  adding 
hydrogen  rather  than  by  taking  away  oxygen. 


88     A    FOUNDATION    COURSE    IN   CHEMISTRY 

owing  to  the  liberation  of  iodine  and  the  combination  of  this 
iodine  with  the  starch  — 


5H2S03  ->  5H2S04  +  H2O  +  I2 

The  oxidation  of  a  solution  of  sulphur  dioxide  may  be 
retarded  by  the  addition  of  small  quantities  of  alcohol, 
glycerine,  or  sugar.1 

Sulphuric  Acid.—  This  is,  perhaps,  the  most  important  acid 
known  in  commerce.  It  is  made  in  this  and  other  countries 
to  the  extent  of  many  thousands  of  tons  yearly.  The  method 
of  manufacture  consists  essentially  in  the  oxidation  of  sulphurous 
acid  ;  but  the  action  of  free  oxygen  alone  is  much  too  slow. 

The  acid  may  be  prepared  from  its  anhydride  sulphur 
trioxide,  SO3,  by  the  addition  of  water.  Although  dry  sulphur 
dioxide  does  not  combine  with  oxygen  under  ordinary  con- 
ditions, its  oxidation  may  be  brought  about  in  contact  with 
certain  porous  substances,  such  as  porcelain,  ferric  oxide,  and 
particularly  platinum  in  a  finely  divided  condition.  When 
sulphur  dioxide  and  oxygen  are  passed  together  over  the  latter 
substance,2  heated  to  a  temperature  of  400°  C.,  they  unite,  and 
sulphur  trioxide  is  formed  — 

SO2  +  O  ->  SO, 

Sulphur  trioxide  is  a  white  crystalline  substance  "  which  dis- 
solves in  water  very  readily,  evolving  much  heat  and  yielding 
sulphuric  acid  — 


To  preserve  it,  it  must  be  kept  in  sealed  glass  tubes. 

In  the  common  commercial  method  for  the  preparation  of 
sulphuric  acid,  nitric  acid  or  one  of  the  oxides  of  nitrogen  is 
used  as  the  oxidising  agent.  The  sulphur  dioxide  is  obtained 
either  by  burning  sulphur  itself  or  more  usually  by  the  com- 
bustion of  iron  pyrites,  FeS*  The  mixture  of  sulphur  dioxide 
and  air  passes  through  a  long  pipe  or  flue,  in  which  any  solid 
particles  are  deposited,  and  from  this,  up  a  tower  (the  Glover 

1  The  preservative  apparently  undergoes  no  change. 

2  The  platinum  remains  unchanged. 

3  This  contains  a  trace  of  moisture.     The  perfectly  pure  trioxide  is  a 
liquid  which  solidifies  at  about  14°  C. 


SULPHUR  89 

Tower),  down  which  crude  sulphuric  acid,  obtained  as  shown 
later,  is  flowing.  The  mixture  of  the  hot  gases  with  the  cold 
acid  cools  them,  concentrates  the  acid,  and  also  frees  it  from 
the  oxides  of  nitrogen  it  contains.  From  the  tower  the  mixed 
gases  (SO2,  air,  and  oxides  of  nitrogen)  pass  into  a  series 
of  large  leaden1  chambers,  where  they  are  mixed  with  steam 
and  vapours  of  nitric  acid,  obtained  by  treating  commercial 
sodium  nitrate  with  concentrated  sulphuric  acid.  The  nitric 
acid  is  reduced,  giving  up  some  of  its  oxygen  to  the  sulphur 
dioxide,  thus  forming  sulphuric  acid — 

*          H2O  +  2SO2  +  2HNO8  ->  2H2SO4  +  N2O3 

The  N2Oo  (nitrous  anhydride)  is  capable  of  oxidising  more 
sulphur  dioxide  to  sulphuric  acid.  As,  however,  nitrous 
anhydride  is  unstable  and  in  the  gaseous  state  consists  largely 
of  nitrogen  peroxide,  NO2,  and  nitric  oxide,  NO,  it  is  con- 
venient to  express  the  reaction  in  terms  of  these  oxides. 

The  nitrogen  peroxide  oxidises  the  sulphur  dioxide,  causing 
the  formation  of  sulphuric  acid — 

2SO2  +  2H2O  +  NO2  ->  2H2SO4  +  NO 

But  nitric  oxide  readily  takes  up  free  oxygen  from  the  air 
(p.  137),  again  forming  nitrogen  peroxide,  which  will  effect  the 
oxidation  of  a  further  quantity  of  sulphuric  dioxide. 

From  this  it  would  seem  that  a  small  amount  of  nitric  acid 
would  oxidise  an  unlimited  quantity  of  sulphur  dioxide ;  but 
there  is  also  a  certain  loss  by  reduction  of  some  of  the  nitrogen 
compounds  to  nitrous  oxide  N2O  (p.  137).  A  still  greater  loss 
would  arise  by  the  carrying  away  of  the  excess  of  oxides  of 
nitrogen  from  the  last  of  the  leaden  chambers  by  the  current 
of  waste  gases  (chiefly  atmospheric  nitrogen)  were  it  not  that 
they  are  made  to  pass  up  a  second  tower  (the  Gay-Lussac  tower), 
down  which  concentrated  sulphuric  acid  is  flowing.  The  acid 
absorbs  the  oxides  of  nitrogen.  This  acid  is  then  sent  by 
means  of  pumps  to  the  Glover  tower,  where  it  meets  with 
fresh  sulphur  dioxide,  and  the  chain  of  reactions  again 
commences.  • 

1  Lead  is  not  acted  upon  by  sulphuric  acid  to  any  great  extent. 


9o     A   FOUNDATION    COURSE   IN    CHEMISTRY 

The  sulphuric  acid  obtained  by  this  process  is  concentrated 
by  heating,  when  it  forms  a  colourless,  oily,  extremely  corrosive 
liquid.  It  rapidly  absorbs  moisture,,  and  is  therefore  often  used 
for  drying  gases.  When  mixed  with  water  considerable  con- 
traction in  volume  occurs,  and  much  heat  is  evolved.  This 
may  be  demonstrated  by  taking  a  long  glass  tube  of  about 
£  inch  diameter,  and  pouring  concentrated  sulphuric  acid  into 
it,  to  the  extent  of  about  one- third  of  the  length  of  the  tube, 
and  then  nearly  filling  up  with  water ;  the  level  of  the  top  of 
the  water  should  be  marked  with  an  indiarubber  ring.  The 
two  liquids  at  first  do  not  mix  owing  to  the  great  density  of  the 
sulphuric  acid  (r8  compared  with  water  as  unity).  If  now  the 
tube  be  closed  with  an  indiarubber  stopper  and  the  liquids 
thoroughly  mixed,  the  tube  becomes  too  hot  to  be  held  in  the 
hand,  and  the  volume  of  liquid  considerably  smaller.1 

Sulphuric  acid,  however,  shows  its  affinity  for  water  even 
more  strongly  in  its  action  upon  wood,  etc.  Wood  and  many 
other  organic  substances  rapidly  char,  owing  to  the  extraction 
of  the  elements  of  water.  Consequently,  it  has  a  strong  corro- 
sive action  on  organic  tissues.  Taken  internally  it  would  cause 
death ;  externally,  it  produces  painful  wounds. 

Sulphuric  acid  is  a  dibasic  acid,  and  forms  two  salts  of  soda, 
Na2SO4  (p.  82)  and  NaHSO4,  sodium  hydrogen  sulphate,  often 
called  sodium  bisulphate.  Most  of  the  sulphates  are  soluble 
in  water,  the  exceptions  being  those  of  lead,  silver,  and 
calcium,  which  are  only  slightly  soluble,  and  those  of  strontium 
and  barium.2 

When  sulphates  are  heated  with  charcoal  they  are  reduced 
to  sulphides  (p.  81). 

When  ferrous  sulphate,  FeSO4.7H2O  (p.  200),  is  strongly 
heated  in  the  air  it  is  oxidised  and  decomposed,  and  sulphur 
trioxide  is  evolved — 

2FeSO4  +£>*->  Fe2O3  -f  2SO3 

The  sulphur  trioxide  combines  with  the  water,  which  is  also 
given  off  to  form  an  acid  of  approximately  the  composition 

1  Care  must  be  taken  in  diluting  concentrated  sulphuric  acid  with 
water  ;  it  is  always  advisable  to  add  the  acid  to  the  water. 

2  BaSO4  is  almost  completely  insoluble  in  pure  water. 


SULPHUR 


H2S2O7.  This  acid  is  the  original  "  Oil  of  Vitriol " ;  it  gives 
off  sulphur  trioxide  as  white  fumes  on  being  heated  gently, 
and  is  therefore  called  fuming  sulphuric  acid.  When  more 
water  is  added  it  forms  ordinary  sulphuric  acid.  A  salt  of  the 
acid  can,  however,  be  prepared  by  the  action  of  heat  upon  the 
acid  sulphates — 

2KHSO4  ->  K2S2O7  +  H2O 

Because  they  are  produced  by  the  action  of  heat,  these  salts 
are  called  pyrosulphates  and  the  acid1  pyrosulphuric  acid  (or 
disulphuric  acid). 

Sulphuretted  Hydrogen. — If  iron  filings  and  sulphur  be 
mixed  together,  and  the  mixture  treated  with  dilute  acid, 
hydrogen  is  evolved,  the  sulphur  present  taking  no  part 
in  the  action.  If  the  iron  filings  and  sulphur  are  heated 
and  made  to  combine,  and  then  treated  with  dilute  acid, 
the  hydrogen  comes  off  combined  with  sulphur.  The  com- 
pound is  a  colourless  gas,  having  a 
most  objectionable  odour  of  putrid  eggs. 
Its  density  compared  with  hydrogen  is 
17,  and  therefore  its  molecular  weight 
is  34 ;  this,  together  with  analysis  of  the 
gas,  has  fixed  its  formula  as  H2S.  It  is 
known  as  hydrogen  sulphide,  or  sulphu- 
retted hydrogen.  The  gas  burns  with  a 
blue  flame  similar  to  that  of  burning 
sulphur ;  the  products  of  combustion  are 
sulphur  dioxide  and  water.  It  is  soluble 
in  water,  to  which  it  imparts  a  slightly 
acid  reaction. 

Sulphuretted  hydrogen  may  be  formed 
by  passing  hydrogen  over  sulphur  at  a 
temperature  of  310°  C,  but  it  is  gene- 
rally produced  by  acting  upon  certain 
sulphides  with  dilute  hydrochloric  acid.  Ferrous  sulphide  is 
generally  employed,  because  it  is  the  least  expensive. 

The  gas  is  very  useful  in  chemical  analysis,  as,  on  being 


FIG.  12. 


Gk.  irvp,  fire. 


92     A   FOUNDATION   COURSE    IN   CHEMISTRY 

added  to  solutions  of  metallic  salts,  it  precipitates  insoluble 
sulphides — 

e.g.     CuSO4  +  H2S  ->  CuS  +  H2SO4 

As  large  quantities  are  often  required,  the  apparatus  (Kipp's 
apparatus)  shown  in  Fig.  12  is  generally  used  for  its  prepara- 
tion. This  apparatus  has  the  advantage  of  causing  the  action  of 
the  acid  on  the  sulphide  to  cease  when  the  gas  is  not  required 
and  the  tap  is  therefore  closed. 

Sulphuretted  hydrogen  is  a  powerful  reducing  agent.  Owing 
to  this  property  it  cannot  be  dried  by  passing  through  sulphuric 
acid,  as  the  acid  is  reduced  by  it,  sulphur  dioxide  and  sulphur 
being  formed — 

H2S  +  H2S04  ->  S  +  2H20  +  S0.2 
K2Cr207  +  8HC1  +  3H2S  ->  2KC1  +  2CrCl3  +  7H2O  +  38 

Most  metals,  including  silver,  become  coated  with  sulphide 
when  exposed  to  the  action  of  the  gas.1 

Sulphuretted  hydrogen  is  an  acid,  like  hydrochloric  acid,  in 
that  it  contains  no  oxygen,  and  its  solution  in  water  is  some- 
times called  hydrosulphuric  acid.  It  is  a  dibasic  acid,  and 
forms  two  salts  with  soda,  NaHS  and  Na2S. 

The  sulphides  of  sodium,  potassium,  and  ammonium,  are 
soluble  in  water. 

Those  of  calcium,  magnesium,  strontium,  barium,  chromium, 
and  aluminium  are  decomposed  by  water,  yielding 
hydroxides. 

Those  of  the  remaining  commoner  metals  are  insoluble  in 
water. 

Allotropy. — Elements  which  exist  in  several  forms  differing 
in  their  chemical  and  physical  properties  and  often  in  appear- 
ance are  said  to  show  "  allotropy." 

The  various  allotropic  modifications  of  an  element  differ  in 
the  amount  of  energy  they  contain,  and  therefore  in  their 
powers  of  reacting  with  other  substances. 

The  preparation  and  properties  of  ozone  throw  light  on 

1  A  similar  action  takes  place  with  other  sulphur  compounds,  such  as 
albumen  (white  of  egg)  or  vulcanised  indiarubber,  both  of  which  contain 
sulphur. 


SULPHUR 


93 


FIG.  13. 


the  nature  of  allotropy.     It  was  mentioned  that  this  substance 
is  formed  when  dry  oxygen  is  subjected  to  the  action  of  the 
electric  spark,  or,  better,  to  that   of  the 
silent  electric  discharge.     The   apparatus 
necessary  for  this  latter  method  of  prepara- 
tion is  shown  in  the  illustration. 

The  central  space  C  in  the  apparatus 
is  bounded  by  two  glass  tubes,  both  of 
which  are  coated  with  some  electrical  con- 
ductor, and  connections  are  made  to  the 
terminals  of  an  induction  machine  as 
shown.  Oxygen  is  supplied  by  the  side 
tube  A,  passes  through  the  space  C,  and 
emerges  from  the  tube  B.  During  the 
passage  it  has  become  ozonised,  that  is, 
partly  converted  into  ozone ;  its  volume 
has  decreased  and  its  oxidising  properties 
greatly  intensified.  It  has  a  strong  odour,1 
bleaches  organic  colouring  matter,  blackens 
a  piece  of  silver  held  in  it,  covering  the  metal  with  a  coating 
of  oxide;  liberates  iodine  from  potassium  iodide,  oxidises 
mercury,  and  rapidly  causes  the  resinification  of  certain  oils 
and  of  turpentine. 

When  passed  through  a  heated  tube  its  volume  is  restored 
to  that  of  the  original  oxygen,  and -it  loses  all  its  specific 
properties  ;  it  is  reconverted  into  oxygen. 

The  above  method  of  preparation  and  decomposition 
shows  that  ozone  consists  entirely  of  oxygen.  But  as  it  cannot 
be  produced  pure  in  this  way  its  composition  can  only  be 
determined  indirectly.  This  has  been  done  as  follows  : — 

A  known  volume  of  ozonised  oxygen  is  divided  into  two 
equal  portions,  A  and  B. 

A  is  treated  with  turpentine,  which  absorbs  the  ozone. 
The  contraction  in  volume  shows  the  amount  of  ozone 
present. 

B  is  heated,  and  the  proper  corrections  having  been  made 
for  temperature  and  pressure,  the  increase  in  volume  is  measured. 
1  This  property  gives  it  its  name.     Gk.  #&«>,  to  smell. 


94    A   FOUNDATION   COURSE   IN   CHEMISTRY 

This  increase  is  due  to  the  conversion  into  oxygen  of  the  same 
amount  of  ozone  as  was  present  in  A.  It  is  found  to  be  one- 
half  of  the  volume,  as  determined  by  the  turpentine  absorption. 

The  experiments  therefore  show  that  ozone,  on  being  con- 
verted into  oxygen,  increases  its  volume  by  one-half,  that  is, 
every  two  volumes  of  ozone  become  three  of  oxygen.  There- 
fore every  two  molecules  of  ozone  become  three  of  oxygen ; 
but  three  molecules  of  oxygen  contain  six  atoms,  and  therefore 
every  molecule  of  ozone  contains  three  atoms  of  oxygen.  It 
is  represented  by  the  formula  O3.  Ozone  is  therefore  an 
allotropic  form  of  oxygen,  differing  from  the  ordinary  form 
in  its  increased  energy  content  (which  extra  energy  has  been 
supplied  to  it  by  the  electric  discharge)  and  in  the  number  of 
atoms  contained  in  each  molecule. 

Although  we  know  little  about  the  number  of  atoms  in  the 
molecule  of  an  element  when  in  the  solid  state,  it  is  probable 
that  explanations  similar  to  the  above  might  be  given  for  the 
allotropic  modifications  of  sulphur  and  other  elements  besides 
oxygen. 


NOTE — The  student  should  now  be  able  to  calculate  the  volume  of  a 
gas  evolved  during  any  reaction. 

The  weight  of  a  litre  of  hydrogen  at  N.T.P.  is  '0898  gram,  or  one 
gram  of  hydrogen  measures  11*12  litres.  We  have  already  shown  that  the 
atomic  weight  of  hydrogen  is  generally  taken  as  unity,  and  we  can  there- 
fore state  that  one  atomic  weight  in  grams  of  hydrogen  measures  11*12 
litres.  If  now  another  gas  is  n  times  denser  than  hydrogen,  then  11*12 
litres  of  that  gas  will  weigh  n  grams.  But  as  n  is  the  density  of 
the  gas,  2n  is  its  molecular  weight,  and  2n  grams  will  measure 
22*24  litres.  So,  uniformly,  a  molecular  weight  in  grams  of  any  gas 
measures  22*24  litres. 

In  the  reaction  represented  by  the  equation 

Cu  +  2H2SO4  ->  CuSO4  +  2H2O  +  SO2 

we  see  that  one  atomic  weight  in  grains  of  copper  reacts  with  two  mole- 
cular weights  in  grams  of  sulphuric  acid  and  yields  one  gram-molecule 
of  sulphur  dioxide.  This  we  may  write  down  at  once  as  measuring  22*24 
litres  at  N.T.P.  We  may  calculate  from  this  the  volume  of  gas  evolved 
with  any  other  weight  of  copper  or  sulphuric  acid  at  N.T.P.  and  then 
make  any  necessary  corrections  for  temperature  and  pressure. 


CHAPTER   XI 

ASHES 

WHEN  animal  or  vegetable  matter  is  burned  in  air,  the 
residue  left  is  known  as  "  Ash."  The  quantity  and  composition 
of  this  ash  depends  to  a  large  extent  upon  the  nature  of  the 
substance  burned.  Bones,  for  instance,  yield  nearly  ten  times 
as  much  ash  as  wood,  and  the  ashes  are  composed  of  very 
different  materials.  Both  of  these  substances — wood  ashes 
and  bone  ash — are  of  great  importance  in  the  arts  and  in 
agriculture. 

Wood  Ashes. — When  timber  is  felled  the  twigs  and  small 
boughs  are  cut  off  and  are  often  burned.  Formerly,  this 
operation  was  carried  out  in  iron  pots  to  facilitate  the  col- 
lection of  the  ashes,  and  the  product  was  therefore  called  "  pot 
ashes."  Nowadays,  both  in  Canada  and  in  the  United  States, 
where  the  process  is  still  carried  on,  it  is  usually  done  in  pits 
dug  in  the  ground,  but  the  name  remains. 

Wood  ashes  contain  from  5  to  10  per  cent,  of  potassium 
carbonate,  which  can  be  separated  almost  completely  from  the 
other  constituents  by  solution  in  water.  The  product  obtained 
on  crystallisation,  and  which  is  called  potash,  contains  50  to 
60  per  cent,  of  potassium  carbonate.  By  a  further  process  of 
solution  and  recrystallisation  a  still  purer  substance  containing 
upwards  of  90  per  cent,  of  potassium  carbonate  can  be  obtained. 
This  is  called  "  pearl  ash  "  or  "  American  ashes." l 

1  Potassium  carbonate  is  chiefly  obtained  from  potassium  chloride, 
which  occurs  in  the  Stassfurt  salt  deposits  assylvite,  KC1,  and  as  carnallite, 
KC1,  MgCl26H,jO.  The  potassium  chloride  is  heated  with  water,  carbon 
dioxide,  and  magnesium  carbonate  under  pressure — 

2KC1  +  aMgCO,  +  C02  +  H20  ->  2KHMg(CO,)2  +  MgCl., 
The  potassium  magnesium  salt  is  decomposed  by  heating  with  water  to  120°, 


96     A   FOUNDATION   COURSE   IN   CHEMISTRY 

Potassium  Carbonate. — This  substance  closely  resembles 
ordinary  washing  soda  in  its  chemical  properties.  Its  composi- 
tion is  represented  by  the  formula  K2CO3.  It  is  usually  sold 
as  an  anhydrous  powder,  but  crystals  of  the  formula 
K2CO33H2O  can  be  formed  from  solution  in  water,  in  which 
it  is  readily  soluble.  Although  a  normal  salt,  its  solution 
exhibits  a  strongly  alkaline  reaction.  Like  other  carbonates, 
it  reacts  with  all  the  common  acids,  forming  the  corresponding 
potassium  salt,  carbon  dioxide  and  water.  Practically  all  the 
other  potassium  salts  can  be  prepared  from  it  in  this  way,  and 
it  was  formerly  the  chief  source  from  which  they  were  obtained. 
Since  the  discovery  of  enormous  deposits  of  potassium  salts — 
chiefly  chloride  and  sulphate — at  Stassfurt  in  Germany,  the 
potassium  carbonate  obtained  from  wood  ashes  is  not  so 
largely  employed. 

Potassium  carbonate  reacts  with  calcium  hydroxide,  forming 
potassium  hydroxide  (caustic  potash).  The  reaction  is  similar 
to  that  for  the  preparation  of  caustic  soda  (p.  82). 

A  large  number  of  potassium  salts  are  used  in  the  industries 
and  in  medicine.  They  closely  resemble  the  corresponding 
sodium  salts.  The  most  important  are  the  sulphate  and  the 
nitrate.  Potassium  sulphate  occurs  in  the  Stassfurt  salt  deposits 
as  schonite,  MgSO4K2SO46H2O,  and  as  kainite,  K2SO4MgS04- 
MgCL6H2O,  from  both  of  which  it  is  extracted  and  is  used 
as  a  potash  manure.  Kainite  is  also  used  for  the  same  purpose, 
but  the  material  supplied  to  the  agriculturist  under  this  name 
seldom  or 'ever  has  exactly  the  composition  represented  by 
the  formula  given  above.  Potassium  nitrate  (p.  136)  is  used 
largely  as  the  chief  constituent  in  black  gunpowder.  Sodium 
nitrate  cannot  be  used  for  this  purpose,  although  it  is  cheaper, 

and  the  precipitated  MgCO3  removed  by  filtering.  KH.Mg(CO3)2  is 
potasium  magnesium  bicarbonate  ;  compare  "temporary  hardness  "(p.  70). 
Potassium  carbonate  is  also  obtained  from  "suint,"  a  fatty  material  which 
forms  a  large  percentage  of  the  weight  of  sheep's  wool,  and  from  which  it 
can  be  obtained  by  washing. 

Root  crops  take  up  large  quantities  of  potash  from  the  soil ;  this  is 
notably  the  case  with  sugar-beet.  The  molasses  left  after  crystallisation  of 
the  sugar  therefore  contains  considerable  quantities  of  the  potassium  salts 
of  organic  acids.  From  these  potassium  carbonate  is  obtained  by  ignition. 
This  forms  another  important  source  of  the  potassium  compounds,  as  the 
sugar-beet  is  very  widely  cultivated  in  Europe. 


ASHES  97 

because  it  absorbs  moisture  from  the  air  and  becomes  damp. 
The  nitrate  is  put  into  gunpowder  to  supply  the  necessary 
oxygen. 

The  metal  potassium  is  obtained  by  strongly  heating 
potassium  carbonate  with  carbon  in  closed  vessels,  when  the 
free  element  distils  over — 

K2C03  +  2C  =  2K  +  3CO 

Special  precautions  must  be  observed  in  this  operation 
to  prevent  the  formation  of  a  compound  of  potassium  with 
the  carbon  monoxide  K6(CO)6,  which  is  highly  explosive. 
An  improved  method  of  obtaining  potassium  consists  of 
heating  potassium  hydroxide  with  carbon  in  the  form  of  iron 
carbide,  made  by  heating  pitch  with  iron  filings.  No  carbon 
monoxide  is  formed — 

6KOH  +  2C  ->  2K2CO3  +  sH2  -f  2K 

Potassium,  a  bright  grey  metal,  is  softer  and  less  dense 
than  sodium,  and  is  even  more  readily  oxidised. 

Bone  Ash. — When  bones  are  burned  the  ash  which  remains 
amounts  to  something  like  half  the  weight  of  the  original 
substance.  It  is  insoluble  in  water  but  dissolves  readily 
in  dilute  hydrochloric  acid,  and  can  be  separated  from  the 
combustible  matter  in  this  way  before  the  bones  are  burnt. 
The  ash  is  in  fact  the  incombustible  mineral  material  which 
the  bones  contain.  The  combustible  matter  which  remains 
after  this  "  decalcifying  "  retains  the  colour,  shape,  and  appear- 
ance of  the  bone,  but  is  found  to  be  soft  and  flexible.  This 
shows  that  the  rigidity  of  bones  is  due  to  the  presence  of  the 
ash  constituents. 

It  can  be  shown  in  various  ways  that  bone  ash  consists 
mainly  of  phosphate  of  lime.  Magnesium  compounds  and 
fluorine  also  enter  into  the  composition  of  the  ash,  but  they 
are  present  in  insignificant  quantities,  and  for  the  present, 
may  be  ignored. 

When  bone  ash  is  mixed  with  carbon  and  silica  and  heated 
in  closed  retorts  in  an  electric  furnace,  phosphorus  distils 
over  and  may  be  collected  under  water — 

Ca3(P04)2  +  3Si02  +  sC  -»  sCaSiOa.  +  5CO  +  2? 

H 


98     A   FOUNDATION   COURSE   IN   CHEMISTRY 

Phosphorus.  —  Prepared  as  above,  phosphorus1  is  a  pale 
yellow,  soft,  wax-like  solid  (sp.  gr.  1*83).  It  melts  at  44°  C, 
a  temperature  much  below  that  of  boiling  water,  and  can  be 
cast  into  any  desired  shape.  For  convenience,  it  is  generally 
sold  in  the  form  of  sticks  of  about  one-third  of  an  inch  in 
diameter.  It  is  intensely  poisonous  ;  even  the  fumes,  when 
inhaled,  give  rise  to  a  painful  disease,  necrosis  of  the  jawbone, 
popularly  called  among  match  workers,  who  are  most  liable 
to  contract  it,  "  phossy-jaw."  The  liability  to  the  disease 
has,  however,  materially  decreased  with  the  more  frequent 
use  of  red  phosphorus  in  the  preparation  of  matches.  The 
temperature  of  ignition  of  yellow  phosphorus  (35°-45°  C.) 
is  much  lower  than  that  of  sulphur  and  other  common  com- 
bustibles ;  in  fact,  phosphorus  vapour  will  take  fire  even  when 
mixed  with  steam.  It  therefore  takes  fire  very  readily  in  the 
air  and  must,  for  this  reason,  be  handled  with  great  care.  The 
wounds  inflicted  by  burning  phosphorus  are  extremely  painful. 
It  is  insoluble  in  water,  and  for  safety  is  invariably  kept 
immersed  in  it.  Yellow  phosphorus  dissolves  readily  in 
carbon  bisulphide  (p.  84).  When  the  solvent  evaporates,  the 
phosphorus  separates  in  the  form  of  crystals.  If  a  small 
quantity  of  the  solution  in  carbon  bisulphide  be  poured  on  a 
piece  of  filter  paper  and  allowed  to  dry,  the  phosphorus 
is  left  in  a  very  finely  divided  condition,  and  takes  fire 
spontaneously. 

Other  modifications  of  phosphorus  are  known.  The  most 
important  is  the  red  or  amorphous  variety.  It  is  dark  chocolate 
red  in  colour,  it  cannot  be  melted,  but  can  be  turned  into 
vapour  by  heating,  which  on  being  condensed  yields  the  yellow 
variety.  When  pure  it  is  not  poisonous.  It  is  insoluble  in 
carbon  bisulphide  and  cannot  be  crystallised.  Red  phosphorus 
does  not  readily  take  fire,  and  may  be  safely  kept  un- 
covered.2 

Yellow  phosphorus  changes  into  the  red  modification  when 


1  Gk.  Qus,  light  ;  <J>e'p«,   I  bear.     It  is  called  phosphorus  because  it 
appears  luminous  in  the  dark. 

2  Red  phosphorus  is  familar  as  the  "striking  part  "  on  boxes  of  so-called 
afety  matches. 


ASHES  99 

heated  to  about  250°  C.  The  change  is  accompanied  by 
considerable  evolution  of  heat  (/.<?.  the  phosphorus  loses 
energy) ;  it  is  greatly  accelerated  by  the  presence  of  a  trace 
of  iodine.  The  effect  of  the  addition  of  iodine  is  complicated 
by  the  formation  of  an  iodide  of  phosphorus.  It  is  clear  from 
the  above  that  the  red  variety  contains  much  less  energy  than 
the  yellow,  and  this  sufficiently  accounts  for  its  comparative 
•inactivity. 

Phosphoric  Anhydride. — When  any  modification  of 
phosphorus  is  burned  in  excess  of  air,  it  combines  with 
oxygen  and  the  oxide  P2O5  is  formed.  The  substance  appears 
in  the  form  of  dense  white  fumes  (p.  16),  which  soon  settle 
on  the  sides  of  the  vessel  as  a  white  powder.  It  is  called 
phosphorus  pentoxide  to  distinguish  it  from  other  known 
oxides  of  phosphorus,  all  of  which  contain  a  smaller  pro- 
portion of  oxygen.  It  is  often  called  phosphoric  acid  by 
farmers  and  others,  but  this  name  is  wrong  and  is  apt  to 
prove  misleading.  The  true  relationship  of  the  pentoxide  to 
phosphoric  acid,  properly  so  called,  is  indicated  by  the  name 
phosphoric  anhydride  (p.  87),  which  is  often  applied  to  it. 

Phosphoric  Acid. — The  oxide  PA  is  highly  deliquescent. 
Its  solution  in  water  is  accompanied  by  the  evolution  of  a 
large  amount  of  heat.  This  shows  that  the  two  substances 
enter  into  chemical  combination  forming  a  hydroxide  just  as 
lime  does.  Calcium  oxide  forms  only  one  definite  hydroxide, 
but  phosphorus  pentoxide  can  unite  with  water  in  three 
different  proportions.  On  evaporating  a  solution  just  after 
it  is  made,  a  glassy  mass  is  left  which  is  known  as  meta- 
phosphoric l  acid.  Its  formula  is  HPO3 

P2O5  -f  H2O  ->  2HP03,  or  P02(OH) 

If  the  solution  be  allowed  to  stand  for  several  days  and 
then  evaporated  the  compound  obtained  has  the  composition 
H3P04 

P205  +  3H20  ->  2H3P04,  or  PO(OH)3 

This    is    known   as   orthophosphoric 2   acid.       The   third 

1  Gk.  jteTo,  besides,  among,  etc. 

2  Gk.  op86s,  right,  true,  correct,  genuine,  etc. 


ioo    A   FOUNDATION    COURSE    IN    CHEMISTRY 

compound,  H4P2O7,  known  as  pyrophosphoric ]  acid,  is  obtained 
by  heating  orthophosphoric  acid  for  some  time  at  a  temperature 
of  255°  C.  when  it  loses  water — 


If  the  pyro  acid  is  dissolved,  it  slowly  recombines  with  the 
water  it  has  lost  and  again  forms  orthophosphoric  acid,  but 
further  heating  of  the  pyro  acid  causes  further  loss  of  water 
and  formation  of  the  meta  acid — 

H4P2O7  -»  2HPO3  -f-  H2O 

Phosphorus  pentoxide  is  therefore  an  acidic  oxide.  Of 
the  three  acids  which  it  forms  with  water,  the  ortho  acid  is  by 
far  the  most  important  and  its  salts  the  commonest.2  All  the 
phosphates  which  occur  in  nature,  e.g.  bone-ash,  coprolite,  etc., 
are  othophosphates. 

Orthophosphates. — When  solutions  of  orthophosphoric 
acid  are  neutralised  with  sodium  hydroxide,  two  of  the  three 
atoms  of  hydrogen  in  the  acid  are  replaced  by  sodium.  The 
composition  of  the  salt  is  represented  by  the  formula  Na2HPO4, 
and  it  is  called  di-sodium  hydrogen  orthophosphate,  or  more 
generally  common  or  neutral  sodium  phosphate.3  If  only  one- 
half  the  quantity  of  sodium  hydrate  is  used,  only  one  of  the 
three  atoms  of  hydrogen  is  replaced  by  sodium.  The  salt 
formed  is  sodium  di-hydrogen  orthophosphate,  NaH2PO4  (acid 
sodium  phosphate).  It  exhibits  an  acid  reaction  in  solution 
in  water.  If  orthophosphoric  acid  be  mixed  with  sodium 
hydroxide  to  the  extent  of  half  as  much  again  as  is  required 
to  form  the  neutral  phosphate,  all  the  three  hydrogens  are 
replaced  and  the  normal  sodium  salt  can  be  formed.  It  is 
strongly  alkaline  and  not  stable  in  solution.  The  formula  of 
the  salt  is  of  course  Na3PO4.4  As  these  three  salts  of  soda 
can  be  formed  from  orthophosphoric  acid  we  say  that  the  acid 
is  tribasic. 

1  Gk.  irvp,  fire. 

2  The  three  acids  must  be  regarded  as  different  kinds  of  phosphonV 
acid  because  they  are  all  formed  from  the  same  acidic  oxide. 

3  Na2HPO4  shows  a  faintly  alkaline  reaction. 

4  As  a  rule,  normal  salts  of  all  but  feeble  acids  are  neutral. 


ASHES    .  .  _  ,(  ..   a    ,1.01. 

The  corresponding  salts  of  other  bases'  can  be  prepared  in 
a  similar  manner.  The  primary,  secondary,  and  normal  phos- 
phates of  potassium  are  represented  respectively  by  the 
formulae  KH2PO4,  K2HPO4,  and  K3PO4.  The  primary  and 
secondary  ammonium  orthophosphates  are  well  known. 
They  are  (NH4)H2PO4  and  (NH4)2HPO3.  The  tertiary  or 
normal  salt  has  not  been  prepared. 

An  important  salt  of  orthophosphoric  acid  is  obtained  by 
adding  a  solution  of  ammonium  chloride  to  one  of  ordinary 
sodium  phosphate  — 

Na2HPO4  +  NH4C1  ->  Na(NH4)HPO4  +  NaCl 

Na(NH4)HPO4  is  then  precipitated  as  crystals  with  four 
molecules  of  water  of  crystallisation.  It  is  known  as  "  Micro- 
cosmic  Salt."  l  It  is  neutral  to  litmus. 

The  phosphates  of  the  alkalies  and  of  ammonium  are  soluble 
in  water.  The  orthophosphates  of  the  diad  bases  (Ca,  Mg, 
etc.),  except  the  primary  salts,  are  insoluble.  They  are  easily 
prepared,  but  owing  to  the  difference  in  the  valency  of  the 
bases,  their  formulae  are  slightly  more  complex.  The  diad 
elements  are  so  called  because  each  atom  replaces  two  atoms 
of  hydrogen.  In  order  to  construct  formulae  for  the  ortho- 
phosphates  of  the  diads,  therefore,  it  is  simpler  to  take  2H3PO4, 
which  is  equal,  quantitatively,  to  H6(PO4)2.2  If  two  atoms  of 
hydrogen  in  this  are  replaced  by  one  atom  of  calcium,  we 
obtain  the  formula  CaH4(PO4)2  for  the  monocalcic  ortho- 
phosphate,  the  calcium  salt  corresponding  to  the  primary 
(acid)  sodium  orthophosphate  3  NaH2(PO4).  If  all  six  atoms 
of  hydrogen  were  replaced  by  three  atoms  of  calcium,  we 
should  obtain  the  formula  Ca3(PO4)2  for  the  normal  or  tri- 
calcic  orthophosphate,  corresponding  to  the  normal  or  tri- 
sodium  phosphate.  The  formula  for  the  intermediate  compound 
corresponding  to  the  secondary  or  di-sodium  orthophosphate 
(Na2HPO4)  might  be  derived  by  substituting  two  atoms  of 


1  Gk.  piKpost  little  ;  /cJtr/ios,  the  world,  universe,  order,  etc. 

2  It  is  not  correct  to  express  the  formula  in  this  way,  though  it  is  con- 
venient to  do  so  now  for  purposes  of  explanation. 

3  This  might  also  be  written—  though  incorrectly—  as  NajjH^POJz  to 
exhibit  the  analogy  between  the  two  compounds. 


502    A   FOUNDATION    COURSE   IN   CHEMISTRY 

calcium  for  four  atoms  of  hydrogen.  This  gives  Ca2H2(PO4)2. 
It  is,  however,  easily  obtained  from  the  ordinary  formula  for 
phosphoric  acid  H3PO4  by  substituting  one  atom  of  calcium 
for  two  atoms  of  hydrogen,  and  is  generally  written  CaHPO4. 

Several  salts  are  known  which  contain  both  diad  and 
monad  bases  in  the  same  molecule.  One  of  these,  magnesium 
ammonium  phosphate,  obtained  when  magnesium  chloride  is 
added  to  the  solution  of  a  phosphate,  in  presence  of  ammonium 
salts  and  ammonia,  is  of  special  importance.  It  is  represented 
by  the  formula  MgNH4PO4.1 

Phosphoric  acid  in  a  soluble  form  is  essential  for  the 
growth  of  plants,  and  in  order  to  supply  it  to  an  exhausted  soil 
bone  ash  is  sometimes  used,  but  it  is  insoluble  and  its  action 
is  therefore  slow.  By  treatment  with  sulphuric  acid,  however, 
the  primary  calcium  phosphate  is  formed — 

Ca3(PO4)2  +  2H2SO4  ->  2CaSO4  +  CaH4(PO4)2 

and  this  salt  is  soluble  in  water.  The  mixture  of  calcium 
sulphate  and  soluble  calcium  phosphate  is  largely  used  as  a 
fertiliser.  It  is  sold  under  the  name  of  "  Superphosphate  of 
lime." 

Effects  of  Heat  on  Orthophosphates. — The  normal  salts 
undergo  no  change  on  heating.  When  any  orthophosphate 
which  contains  hydrogen  atoms  or  ammonium  is  heated,  the 
hydrogen  atoms  are  expelled  in  combination  with  oxygen,  as 
water,  and  the  ammonium  is  volatilised  as  ammonia  gas. 
Remembering  this,  it  is  easy  to  see  what  is  left  in  each  case. 
A  few  examples  will  make  this  plain. 

NaH2PO4  ->  NaPO3  +  H2O 
-      2Na2HPO4  ->  Na4P2O7  +  H2O 
NaNH4HPO4  ->  NaPO3  +  H2O  +  NH:! 
2MgNH4PO4  ->  Mg2P2O7  +  H2O  +  2NH:; 
(NH4)2HP04->HP03  +  H20  +  2NH3 

It  is  now  possible  to  return  to  the  preparation  of  the 
element  phosphorus  and  explain  the  reactions  by  which  it  is 
obtained. 

1  It  is  of  importance  in  the  quantitative  estimation  of  phosphoric  acid. 


ASHES  103 

Bone  ash  and  coprolite  consist  essentially  of  tricalcic 
phosphate,  Ca3(PO4)2.  This  compound  undergoes  no  change 
when  heated,  either  alone  or  with  charcoal.  When  acted 
upon  by  sulphuric  acid,  the  calcium  atoms  may  be  successively 
withdrawn  according  to  the  equations — 

(a)  Ca3(P04)2  -f  H2S04  ->  CaSO4  +  Ca2H2(PO4)2 

i.e.  2CaHP04 

(b)  Ca3(P04)2  +  2H2S04  -»  2CaSO4  +  CaH4(PO4)2 

(c)  Ca3(P04)  +  3H2S04-»3CaS04  +  2H:5PO4 

The  substances  obtained  in  reactions  (b)  and  (c)  can  be 
used  for  the  preparation  of  phosphorus.  Both  monocalcic 
phosphate  and  orthophosphoric  acid  lose  water  when  heated 
strongly — 

(b)  CaH4(P04)2  ->  Ca(P03)2  +  2H2O 

(c)  H3PO4->HP03  +  H20 

forming,  respectively,  calcium  metaphosphate  and  metaphos- 
phoric  acid.  If  either  of  these  substances  be  heated  with 
carbon,  it  is  reduced  and  free  phosphorus  is  liberated  and 
distils  over — 

(b)  sCa(PO3)2  +  loC  ->  Ca3(PO4)2  +  ioCO  +  P4 

(c)  2HPOS  +  6C  ->  6CO  +  2P  +  H2 

The  action  may  perhaps  be  better  understood  if  we 
remember  that  metaphosphoric  acid  is  P2O5.H2O,  and  that 
orthophosphoric  acid  is  P2O5.3H2O.  It  is  obvious  that 
the  corresponding  calcium  salts  may  be  considered  as 
CaO.P2O5  and  3CaO,  P2O5  respectively.  The  changes  can 
then  be  represented  in  diagrammatic  fashion  as  follows  : — 


CaO  .        P205 

CaO  . 
CaO  . 


+     ioC 


The  action  which  takes  place  in  the  method  for  the  pre- 
paration   of  phosphorus   given   on   page   97   should  now  be 
.  intelligible;    looking   on   Ca3(PO4)2  as   equivalent   to   3CaO, 


104     A  FOUNDATION    COURSE  IN   CHEMISTRY 

P2O5,  the  silica,  which  is  an  acidic  oxide,  has  combined  with 
the  calcium  oxide,  CaO  +  SiO2  ->  CaSiO3,  and  the  liberated 
phosphorus  pentoxide  has  been  reduced  by  the  carbon.  When 
phosphorus  pentoxide  itself  is  heated  with  carbon  it  under- 
goes reduction,  and  the  phosphorus  is  liberated  as  shown  in  the 
equation — 

2P2O8  +  ioC->ioCO+P4 

When  phosphorus  is  oxidised  in  a  limited  supply  of  air  the 
trioxide  is  formed.  The  vapour  density  of  this  compound 
shows  that  it  must  be  represented  by  the  formula  P4O6.  It 
combines  with  water  forming  phosphorous  acid  H3PO;{. 
This  acid,  although  it  contains  three  atoms  of  hydrogen,  is 
dibasic,  only  two  of  the  hydrogen  atoms  being  replaceable  by 
a  metal. 

When  phosphorous  acid  is  heated  it  decomposes — 

4H,PO,-»3HP08  +  3H20  +  PH3 

The  compound  PH3,  phosphine  or  phosphoretted  hydrogen, 
is  generally  prepared  by  boiling  phosphorus  with  a  strong 
solution  of  caustic  soda  or  potash — 

3KOH  +  4P  +  3H20  ->  3KH2PO2  +  PH3 

The  compound  KH2PO2  is  the  potassium  salt  of  hypo- 
phosphorous  acid  H3PO2.  This  acid,  although  it  contains  three 
atoms  of  hydrogen,  is  monobasic.  One  of  the  hydrogen  atoms 
only  can  be  replaced. 

Phosphine  (PH3)  is  a  colourless  gas  with  a  peculiar  odour. 
It  is  insoluble  in  water  and  readily  takes  fire.  In  fact,  the  gas 
given  off  by  the  above  reaction  is  spontaneously  inflammable;, 
this,  however,  is  due  to  the  presence  of  small  quantities  of 
another  compound,  liquid  phosphoretted  hydrogen,  P2H4. 

Phosphine  can,  under  certain  conditions,  combine  with 
HC1,  HBr,  and  HI,  but  at  the  ordinary  temperature  and 
pressure  the  compounds  are  not  stable.  They  are  PH4C1, 
PH4Br,  PHJ,  and  are  known  as  phosphonium  chloride, 
bromide,  and  iodide  respectively.1 

1  These  compounds  are  of  but  little  importance.  The  action  of 
phosphine,  however,  in  forming  these  compounds  should  be  compared  with 
that  of  ammonia  (q.v.  p.  127). 


CHAPTER   XII 

SAND,    CLAY,    ETC. 

"  SAND  "  and  "  clay  "  are  popular,  not  scientific,  terms.  They 
are  not,  therefore,  capable  of  scientific  definition.  Any  mass  of 
small,  gritty,  angular  fragments  of  minerals  is  popularly  termed 
sand.  The  fragments  may  be  all  of  one  kind.  More  fre- 
quently the  mass  consists  of  several  different  kinds  mixed 
together,  but  some  particular  mineral  generally  predominates. 

Quartz  is  one  of  the  commonest  of  rock-forming  minerals, 
and  as  it  is  extremely  hard  and  resistant  to  all  kinds  of 
chemical  change,  it  usually  forms  a  large  proportion  of  any 
deposit  of  sand.  Sea  sand  often  consists  almost  exclusively 
of  fragments  of  quartz. 

The  only  definite  characteristic  of  sand  is  grittiness.  This 
property  which  depends  upon  the  size  of  the  fragments  would 
not  generally  be  recognised  in  material  consisting  of  particles 
greater  than  about  y^  or  less  than  y^  of  an  inch  in  diameter. 
Material  consisting  of  larger  particles  would  generally  be 
called  gravel.  When  the  particles  are  smaller  than  about  y^ 
part  of  an  inch  they  are  practically  impalpable,  and  when  moist 
cohere  strongly  together,  forming  a  plastic  mass  which  is 
commonly  called  "  clay." 

Occasionally  the  term  "pure  clay"  is  used  to  signify 
purified  kaolin  (china  clay),  H4Al2Si2O9,  and  similarly  the  term 
"  pure  sand  "  to  mean  quartz  particles,  SiO2.  But  in  view  of 
what  has  been  said  above  it  is  obvious  that  the  words  "  sand  " 
and  "  clay  "  should  not  be  used  with  reference  to  the  chemical 
nature  of  the  substances,  but  only— if  at  all— with  reference 
to  the  size  of  the  particles. 


io6    A   FOUNDATION   COURSE   IN  CHEMISTRY 

Most  of  the  rock-forming  minerals  are  silicates,  and, 
although  insoluble,  they  are  slowly  acted  upon  by  water, 
carbon  dioxide,  etc.  When  finely  pulverised,  they  undergo 
chemical  change  relatively  quickly,  forming  soluble  compounds 
and  colloidal  hydrates.  The  latter  are  generally,  but  not 
necessarily,  present  in  clay  in  considerable  quantities  and  tend 
to  increase  its  plasticity. 

The  crystalline  mineral,  quartz,  is  the  oxide  of  an  element 
known  as  silicon.1  It  has  the  composition  SiO2  and  is  often 
called  silica.2 

Silicon  is,  next  to  oxygen,  the  most  plentiful  element  in 
the  crust  of  the  earth.  It  may  be  obtained  by  the  reduction 
of  the  oxide  with  metallic  magnesium — 

2Mg  +  SiO2->Si-h  2MgO 

A  certain  amount  of  magnesium  silicide,  Mg2Si,  is  formed 
at  the  same  time.  The  oxide  can  also  be  reduced  by  carbon 
in  the  electric  furnace.  The  free  element  is,  however,  of  but 
little  importance. 

When  the  oxide  SiO2  is  fused  with  sodium  carbonate,  it 
displaces  the  carbon  dioxide  and  forms  a  compound  called 
sodium  silicate — 

Na2COa  +  Si02  ->  Na2Si03  +  CO2 

Sodium  silicate  is  soluble  in  water.  It  is  the  substance 
commonly  sold  under  the  name  of  water  glass.3 

When  hydrochloric  acid  is  added  to  a  dilute  solution  of 
sodium  silicate,  silicic  acid  is  precipitated  as  a  whitish  semi- 
transparent  jelly.  If,  however,  a  dilute  solution  of  sodium 
silicate  is  added  to  hydrochloric  acid  the  silicic  acid  is  not 

1  From  Latin  silex,  flint.  Flint  is  a  mixture  of  crystalline  and 
amorphous  silica. 

8  Quartz  is  extensively  used  for  spectacle  lenses.  It  is  peculiarly  opaque 
to  heat  rays,  but  highly  transparent  to  the  so-called  "  actinic  "  rays  (ultra- 
violet). It  is  also  used  for  making  test-tubes,  flasks,  and  other  chemical 
apparatus.  Such  quartz  vessels  can  be  plunged  into  water  when  red  hot 
without  cracking. 

8  A  solution  in  water  is  used  as  an  egg  preservative.  The  eggs  are 
dipped  in  the  solution  ;  when  dry,  they  become  covered  with  an  air-tight 
coating  of  the  silicate. 


SAND,   CLAY,    ETC.  107 

thrown  down.1  It  can  be  separated  from  the  sodium  chloride 
formed,  and  from  the  excess  of  hydrochloric  acid,  by  a  process 
known  as  dialysis. 

The  solution  is  placed  in  a  vessel  similar  to  A,  as  shown  in 
the  figure,  which  is  then  suspended  in  water.     The  bottom  of 
the   vessel   A   is    made   of  parchment. 
After  some  days  it  will  be  found  that 
the  whole  of  the  sodium  chloride  and 
hydrochloric  acid  have  passed  into  the 
water  in  the  larger  vessel,  while  nothing 
but  silicic  acid  in  solution  remains  in  A. 
Substances   which   thus   refuse   to  pass  pIG>  I4 

through    a    parchment    membrane   are 
non-crystalline,    gluey    materials.      They   have   been    called 
colloids.2     Other  substances  will  pass  through  such  a  mem- 
brane.    Hence,  the  process  of  separation. 

A  colloidal  solution  differs  from  an  ordinary  solution  in 
several  ways.  It  freezes  and  boils  at  practically  the  same 
temperatures  as  the  pure  solvent  (p.  116).  It  can  be  shown, 
in  fact,  that  the  substance  is  simply  suspended  in  the  "  solvent," 
although  in  far  too  fine  a  state  of  division  to  be  visible,  or 
separated  by  ordinary  filtration.  Other  insoluble  substances 
may  be  obtained  in  the  form  of  colloidal  "  solutions  " ;  such 
are  ferric  hydroxide,  alumina,  and  even  certain  metals,  such 
as  gold  and  silver. 

The  silicic  acid  present  in  the  colloidal  "  solution "  is 
thought  to  be  orthosilicic  acid,  H4SiO4.  On  evaporation 
to  dryness,  an  amorphous  glassy  mass  is  left  which  only 
partially  dissolves  in  water,  but  neither  this  nor  the  pre- 
cipitated silicic  acid  corresponds  to  the  formula  H4SiO4. 
Further  heating  drives  off  all  the  water,  and  silicon  dioxide, 
SiO2,  is  left. 

The  formula  of  the  acid  corresponding  to  the  salt  Na2SiO:, 
is  of  course  H2SiO3,  and,  by'  careful  evaporation,  the  colloid 
"  solution,"  obtained  as  above,  could  be  evaporated  till  the 

1  On  mixing  strong  solutions  the  gelatinous  precipitate  is  always  thrown 
down. 

2  Gk.  KoAAo,  glue. 


io8    A    FOUNDATION   COURSE   IN   CHEMISTRY 


composition  corresponded  to  that  formula  ;  but  this  compound 
cannot  be  separated. 

The  rock-forming  minerals  apparently  include  salts  of 
several  silicic  acids.  A  very  few  correspond  to  the  hypo- 
thetical acid  HaSiO3.  Estatite  and  Wollastonite  are  examples, 
the  formulae  of  the  pure  substances  being  MgSiOg1  and 
CaSiO,.1 

Olivine  2  is  also  a  silicate  of  magnesium,  but  the  composi- 
tion of  the  mineral  is  represented  by  the  formula  Mg2SiO4. 
This  corresponds  to  the  hypothetical  orthosilicic  acid 
previously  mentioned. 

The  formulas  for  ortho-  and  meta-  silicic  acids  can  be 
represented  thus— 

OH 


It  has  been  suggested  that  by  the  withdrawal  of  one  molecule 
of  water  from  two  molecules  of  each  of  these  acids,  two 
disilicic  acids  can  be  formed  — 


/OH 

/OH 
(a)     Si<oli 

XO:H! 


-     H.,0 


OH 
OH 
NJH 


(/,)     Si^OH 


/OH 
SifOH 
I  \OH 
Q 

|  /OH 
SiOH 


H8Si,O7 


-     HoO 


Orthodisilicic  acid. 

Si^OH 

=     O  i 

Si^-OH 


Meudisilicic  acid. 


1  These,  at  any  rate,  are  their  simplest  formulae. 

2  Olivine  is  used  in  jewellery  under  the  name  of  "peridot. 


SAND,   CLAY,    ETC.  109 

Also  that  by  the  extraction  of  four  molecules  of  water  from 
three  molecules  of  the  ortho  acid  a  trisilicic  acid  is  formed  — 


Si—  OH 
XOHi  I 


/OH  I XOH 

Si<OH       -     4H20     =      Si/ 

S-5,  |    X)H 

O 

/OH  Si^-OH 

l5ojHi 
lOHj 

These  formulae  afford  a  fairly  simple  explanation  of  the 
composition  of  some  of  the  naturally  occurring  siliceous  minerals, 
though  many  of  them  are  too  complex  to  be  explained  in  this 
way ;  some  probably  contain  more  than  one  type  of  silicic 
acid,  and  others  are  probably  acid  or  basic  salts. 

The  following  are  some  of  the  commoner  silicates  occurring 
in  nature : 

(1)  Mica1   (Muscovite),   K.HaAl3(SiO4)3.     This  could  be 
•formed  from  three  molecules  of  orthosilicic  acid. 

(2)  Kaolinite,2  H2Al2(SiO4)2.H;O.      A  hydrated  silicate  of 
aluminium ;  it  could  be   formed  from  two  molecules  of  the 
orthosilicic  acid. 

(3)  Felspar  (orthoclase),  K.Al.Si3O8.     Probably  a  trisilicate. 

(4)  Serpentine,      Mg3Si2O7.2H2O.       Probably     an    ortho- 
disilicate. 

(5)  Meerschaum,  Mg2H4Si3O10.    Probably  Mg2Si3O8.2H2O, 
hydrated  magnesium  trisilicate. 

(6)  Asbestos.     This  is  really  a  technical  term ;  most  of  the 

1  Distinguished  by  its  perfect  cleavage.     It  is  largely   used  for  lamp 
chimneys  and  electric  insulation. 

2  Kaolinite  was  considered  to  be  present  invariably  as  the  chief  sub- 
stance in  kaolin,  or  china  clay.     It  is  now  thought  probable  that   other 
hydrated  silicates  of  aluminium  may  take  its  place. 


no    A   FOUNDATION   COURSE  IN   CHEMISTRY 

material  known  in  trade  as  "  asbestos  "  is  the  fibrous  variety 
of  serpentine.1 

(7)  Talc,  H2Mgs(SiO,)4.  This  material  when  powdered 
forms  what  is  known  as  "  French  chalk." 

Kaolin  2  is  formed  during  the  weathering  of  granite  rocks, 
owing  to  the  action  of  carbon  dioxide  and  water  upon  the 
felspar. 


2KAlSi,O8  +  2H2O  +  CO,-»  H4Al,SiA  +  4SiO,  +  K2CO, 

This  is,  however,  not  the  only  mode  of  production  ;  besides 
felspar  many  other  siliceous  minerals,  poor  in  magnesium, 
give  kaolin  under  the  action  of  the  atmosphere.  As  the  above 
equation  shows,  kaolin  generally  contains  free  silica  (amorphous 
and  hydrated),  and  often  also  particles  of  quartz.  It  is  found 
mixed  with  compounds  of  iron,  calcium,  and  magnesium,  when  it 
forms  brick  earth,  pipeclay,  etc.  These  are  largely  used  in 
the  making  of  bricks,  tiles,  and  various  kinds  of  coarse  pottery, 
while  the  purer  kaolin  or  china  clay  forms  the  chief  material 
in  the  manufacture  of  porcelain.3 

All  kinds  of  clay  form  a  stiff  plastic  mass  with  water,  which 
can  be  moulded  into  any  required  shape.  When  dried  it  shrinks 
considerably,  and  on  being  strongly  heated  (fired)  it  shrinks 
still  further,  and  forms  an  almost  infusible  mass  which  is  not 
attacked  by  water  or  acids,  and  which  can  no  longer  be  made 
into  a  paste  with  water.  It  is  in  this  way  that  bricks,  pottery, 
and  porcelain  are  made.  The  presence  of  iron  in  the  clay 
causes  the  red  colour  of  the  burnt  material,  as  seen  in  brick, 
in  many  forms  of  common  pottery,  and  in  terra-cotta. 

As  burnt  clay  is  very  porous,  pottery  of  all  kinds  is  generally 
glazed.4  For  this  purpose  salt  is  thrown  into  the  oven  in 
which  the  pottery  is  being  fired.  The  steam  which  the  clay 

1  Owing  to  the  fibrous  nature  of  "  asbestos  "  it  can  be  woven  into  cloth 
or  felted  ;    its  infusibility  and  poor  conductivity  for  heat  cause  it  to  be 
used  for  packing  steam  tubes  and  incombustible  fabrics. 

2  Kaolin  is  the  Chinese  name  for  the  material.     The  words  kao-ling 
are  said  to  mean  "high  ridge  "and  to  be  the  name  of  a  hill  where  the 
clay  was  found.  , 

*  For  making  porcelain,    pure  kaolin  is  mixed  with  finely  powdered 
quartz  and  felspar. 

*  China  and  porcelain,  before  glazing,  is  technically  known  as  "biscuit." 


SAND,   CLAY,   ETC.  in 

gives  off  hydrolyses  the  salt,  giving  NaOH  and  HC1,  and  the 
alkali  combines  with  some  of  the  silica  forming  a  fusible  silicate, 
which  melts  and  on  cooling  covers  the  pottery  or  brick  with 
a  hard  glassy  film.  Red  lead  is  also  used  for  glazing.  This 
causes  the  formation  of  lead  silicate.  For  porcelain,  the 
unglazed  material  is  covered  with  a  thin  cream  of  powdered 
felspar  and  water,  dried  and  heated  to  a  white  heat.  The 
felspar  melts  and  penetrates  the  porcelain  in  all  directions, 
forming  a  thoroughly  adherent  glaze. 

Glass. — This  is  essentially  a  mixture  of  calcium  silicate 
with  silicates  of  potash  or  soda.  It  is  made  by  heating 
together  sodium  carbonate,  powdered  limestone  and  quartz 
sand.  The  composition  of  the  product  is  approximately 
represented  by  the  formula  CaO.Na2O.6SiO2.  Glasses,  how- 
ever, vary  greatly  in  composition ;  sometimes  oxides  of  heavy 
metals,  particularly  that  of  lead,  are  added  to  the  glass,  while 
all  coloured  glasses  contain  silicates  of  other  metals,  such  as 
iron,  cobalt,  and  copper."^  Molten  glass  has,  moreover,  the 
power  of  forming  a  colloidal  "  solution  "  of  certain  of  the 
metals,  notably  gold  and  copper,  both  of  which  impart  a  deep 
ruby  tint  to  it.  Many  varieties  of  glass  also  contain  borates. 

Glass  is  almost  unacted  upon  by  acids ;  it  is,  however, 
appreciably  attacked  by  pure  water,  and  alkalies  corrode  it 
very  considerably. 

Ultramarine. — This  is  a  deep  blue  material  used  as  a 
pigment,  for  laundry  blue,  etc.  It  is  now  prepared  by  heating 
together  kaolin,  sodium  carbonate,  sulphur,  and  charcoal. 
The  composition  approximates  to  the  formula  Na2S2  4NaAlSiO4. 
The  cause  of  the  colour  is,  however,  unknown. 

Formerly  it  was  prepared  by  powdering  the  natural  blue 
mineral  "  lapiz-lazuli,"  which  has  a  similar  composition. 

Carborundum. — This  compound  of  silicon  is  of  great  value 
for  grinding  and  polishing.  It  is  made  by  heating  together  in 
an  electric  furnace,  quartz  sand  and  coke,  with  common  salt — 

SiO2  +  3C->SiC  +  2CO 

As   the   formula   (SiC)   shows,  the   compound   is   carbide  of 
silicon.     It  forms  dark,  almost  black  crystals,  and  is  often 


ii2    A   FOUNDATION   COURSE   IN   CHEMISTRY 

sold  as  a  black  glittering  powder.  When  perfectly  pure  it  is 
colourless.  It  is  almost  as  hard  as  diamond. 

Fluorine. — The  element  silicon  and  its  compounds  are 
readily  attacked  by  fluorine,  and  by  hydrofluoric  acid. 

The  element  fluorine  is  found  combined  with  calcium  as 
fluor  spar,  the  only  fluorine  mineral  which  occurs  in  really 
large  quantities.  It  is  calcium  fluoride,1  CaF2.  When  this, 
or  any  other  fluoride,  is  heated  with  sulphuric  acid  hydro- 
fluoric acid  is  given  off  as  a  gas— 

CaF2  +  H2SO4  ->  CaSO4  4-  H2F2 

As  hydrofluoric  acid  boils  at  19°  C.,  it  could  be  condensed 
in  a  sukable  receiver.  The  anhydrous  acid,  however,  has  no 
industrial  application,  but  the  solution  in  water  is  largely  used 
for  etching  glass.  Owing  to  its  powerful  action  upon  siliceous 
material  it  cannot  be  kept  in  glass  bottles,  and  vessels  for 
containing  it  are  made  of  gutta-percha,  or  sometimes  of 
vegetable  wax  or  paraffin  wax,  botli  of  which  resist  the  action 
of  the  acid. 

Care  must  be  taken  in  handling  the  acid.  The  gas  is 
most  irritating  and  dangerous.  A  strong  solution  in  water 
produces  painful  wounds  which  are  very  difficult  to  heal. 

The  acid  differs  from  the  other  halogen  acids  (p.  79), 
in  that  it  is  dibasic,  and  therefore  two  salts  of  potassium  are 
known,  KHF2  and  KaF2.  Its  use  for  etching  glass  depends 
upon  its  action  upon  silica — 

SiO2  +  2H2F2->SiF4  4-  2H2O 

The  compound  SiF4,  silicon  tetrafluoride,  can  be  prepared  by 
heating  a  mixture  of  sand  or  powdered  glass,  fluor  spar,  and 
concentrated  sulphuric  acid.  It  is  a  gas  which  is  immediately 
decomposed  on  contact  with  water — 

3SiF4  4-  4H2O-»  (SiO2  4-  2H2O)  +  sHaSiFe 

The  silica,  combined  with  water,  perhaps  as  H4SiO4  (ortho- 
silicic  acid),  is  precipitated  and  can  be  filtered  off,  leaving  a 
solution  of  hydrofluo-silicic  acid. 

1  It  is  found  largely  in  Derbyshire,  and  is  hence  known  as  "  Derbyshire 
Spar,"  also,  owing  to  its  being  often  coloured  bright  violet,  as  "Blue  John." 


SAND,  .CLAY,   ETC.  113 

Fluorine1  itself  is  a  most  active  element  and  extremely 
difficult  to  obtain  in  a  free  state.  It  has  been  prepared  by 
the  electrolysis  of  anhydrous  hydrofluoric  acid,  to  which 
potassium  hydrogen  fluoride  is  added  to  impart  electric  con- 
ductivity. The  preparation  must  be  carried  out  in  apparatus 
made  of  platinum  2  and  fluor  spar. 

Fluorine  combines  with  all  the  other  elements  except  oxygen. 
It  decomposes  water  immediately,  liberating  oxygen  partly  in 
the  form  of  ozone  (p.  93). 

Boron. — This  element  is  similar  in  many  of  its  properties 
to  silicon,  although  it  is  more  closely  related  to  aluminium, 
being  always  trivalent.  It  is,  however,  distinctly  non-metallic 
in  character,  and  its  oxide  is  entirely  acidic. 

It  occurs  in  nature  combined  with  oxygen  and  hydrogen, 
or  certain  metals,  as  boric  acid  and  its  salts. 

Boric  acid  is  found  in  the  "  suffioni " 3  of  Tuscany.  The 
most  important  natural  borate  is  borax,  Na2B4O7,4  the  sodium 
salt  of  pyroboric  acid. 

Borax  is  soluble  in  water,  and  when  in  solution  is 
decomposed  by  sulphuric  or  hydrochloric  acid,  boric  acid " 
separating  as  flat  pearly  looking  crystals. 

Na2B407  +  H2S04  +  sH2O  ->  Na2SO4  +  4H3BO3 

Three  boric  acids  are  known.  That  having  the  composition 
H3BO3  is  called  orthoboric  acid,  its  salts  are  almost  unknown. 
When  heated  to  100°  C.  it  slowly  loses  water  and  is  con- 
verted into  metaboric  acid  HBO2.  Heating  to  140°  C. 
causes  the  formation  of  pyroboric  acid  (known  also  as  tetra- 
boric  acid) — 

4HBO2  -  H2O  ->  H2B4O7 

1  Lat.  fluo,  I  flow.     Fluorine  derives  its  name  from  fluor  spar.     This 
mineral  has  been  used  for  a  long  time  as  a  flux  in  metal  smelting,  as  it  pro- 
duces a  fusible  slag. 

2  Copper  or  lead  is  sometimes  used,  as  these  metals  are  soon  covered 
with  a  protecting  coating  of  fluoride. 

3  These  are  jets  of  steam  issuing  from  the  ground. 

4  The  mineral  sometimes  known  as  "  Tincal."     Borax  is  generally  sold 
as  a  crystalline  material  of  the  composition  Na2B4O7ioH2O.     The  hydrate 
Na2B4O75H2O  is  also  sometimes  placed  on  the  market. 

5  Boric  acid  is  sometimes  called  boracic  acid. 


ii4     A   FOUNDATION   COURSE   IN   CHEMISTRY 

Further  heating  drives  off  the  whole  of  the  water  and  leaves 
boric  anhydride,  B2O3,  as  a  glassy  mass. 

As  boric  acid  is  a  very  feeble  acid,  a  solution  of  borax  is 
largely  decomposed  (hydrolysed)  by  water,  so  that  it  gives  a 
strongly  alkaline  reaction,  and  when  warmed  with  fats  will 
saponify  them  (p.  165). 

The  presence  of  the  acid  can  be  detected  by  mixing  the 
suspected  substance  with  alcohol  and  sulphuric  acid,  and  setting 
fire  to  the  alcohol ;  the  flame  will  be  tinged  green  if  boric 
acid  be  present. 

Boric  acid  also  colours  turmeric  paper  brown.1  If  caustic 
soda  be  then  added,  the  brown  colour  is  changed  to  dark  blue 
or  black. 

Boric  acid  and  other  mixtures  of  boric  acid  and  borates 
are  largely  used  as  antiseptics  and  food  preservatives.2 

Borax  melts  when  strongly  heated,  forming  a  clear  trans- 
parent glassy  material,  and  when  molten  has  the  power  of 
dissolving  various  metallic  oxides,  which  impart  to  it 
characteristic  colours. 

When  hydrogen  peroxide  (p.  59)  is  added  to  borax  in 
the  presence  of  excess  of  caustic  soda,  sodium  perborate, 
NaBO34H2O,  crystallises  from  the  solution.  It  is  soluble  in 
water,  but  on  warming  decomposes  with  evolution  of  oxygen. 
It  is  extensively  used  as  a  bleaching  agent  in  laundries. 


APPENDIX  TO   CHAPTER  XII 

Osmotic  Pressure. — The  phenomena  due  to  osmotic  pressure 
are  connected  with  the  process  of  dialysis  described  in  the 
foregoing  chapter. 

All  solutions  are  capable  of  exerting  osmotic  pressure,  and  the 

1  Alkalies  also  turn  turmeric  paper  brown,  but  in  this  case  caustic  soda 
of  course  causes  no  further  change. 

2  In  using  food  preservatives,  it  should  be  noted  that,  in  addition  to  any 
other  physiological  effect  the  preservative  may  have  as  a  drug,  its  presence 
will  always  tend  to  impede  digestion.     It  may  be  necessary  sometimes  to 
employ  a  preservative,  and  boric  acid  seems  to  be  one  of  the  least  harmful. 
It  has  been  suggested  that  cream  might  safely  contain  0*25  per  cent,  and 
margarine  and  butter  0*5  per  cent,  of  boric  acid.     On  no  account  should  any 
preservative  be  present  in  food  for  young  children. 


SAND,   CLAY,   ETC.  115 

result  is  a  tendency  on  the  part  of  the  solution  to  attract  more  of 
the  solvent,  and  so,  to  expand. 

If  we  take  a  glass  tube,  close  it  at  one  end  with  a  piece  of 
membrane  such  as  ordinary  bladder,  and  after  having  poured  into 
it  a  small  quantity  of  a  solution  of  common  salt,  place  it  upright 
in  a  vessel  of  water  with  the  closed  end  immersed,  the  liquid  in  the 
tube  will  rise.  Water  passes  through  the  membrane  into  the  tube, 
and  at  the  same  time  a  small  quantity  of  salt  passes  in  the  opposite 
direction.  If  instead  of  using  a  piece  of  bladder,  we  employed  a 
membrane,  which,  while  allowing  free  passage  of  water,  totally 
prevented  the  passage  of  the  dissolved  substance,  the  height  to 
which  the  water  would  rise  would  be  greater.  Pzeffer  in  1877  per- 
formed experiments  with  various  membranes  and  found  that  the 
most  effective  was  a  freshly  precipitated  film  of  copper  ferrocyanide. 
This  is  freely  permeable  for  water,  but  practically  impermeable  for 
substances  of  high  molecular  weight,  such  as  sugar.  A  membrane 
possessing  such  properties  is  said  to  be  semi-permeable.  A  cell 
containing  the  copper  ferrocyanide  film  can  be  prepared  as  follows  : 
a  porous  (unglazed)  earthenware  jar  is  first  placed  under  an  air- 
pump  and  all  the  air  removed  from  its  pores  ;  it  is  put  into  a 
dilute  solution  of  copper  sulphate,  and  filled  with  a  dilute 
solution  of  potassium  ferrocyanide.  The  liquids  meet  in  the 
wall  of  the  jar  and  produce  by  their  interaction  a  precipitate  of 
copper  ferrocyanide.  If  the  cell  thus  prepared  be  filled  with  a 
solution  of  cane  sugar  and  put  into  a  jar  of  pure  water,  water  will 
pass  through  the  cell  wall  into  the  sugar  solution,  but  the  sugar 
will  not  pass  outwards.  If  when  the  cell  is  filled,  it  is  closed,  and 
fitted  with  a  manometer,  or  instrument  for  measuring  pressure,  it 
will  be  found  that  the  influx  of  water  into  the  solution  will  cause  a 
very  remarkable  increase  of  pressure.  Thus  a  one  per  cent, 
solution  of  sugar  at  a  temperature  of  15°  C.  causes  a  pressure  equal 
to  about  540  millimetres  of  mercury,  i.e.  nearly  three-quarters  of  an 
atmosphere.  This  pressure  must  be  caused  by  the  substance  in 
solution,  for  if  pure  water  be  used,  no  such  increase  of  internal 
pressure  can  be  discovered. 

This  pressure  is  known  as  osmotic  pressure,  and  it  has  been 
found  to  conform  to  the  following  laws,  (a)  It  increases  in  pro- 
portion to  the  concentration  ;  (b)  It  is  proportional  to  the  absolute 
temperature  ;  (c)  If  two  solutions  give  the  same  osmotic  pressure 
their  concentrations  are  proportional  to  the  molecular  weights  of 
the  substances  dissolved.  Comparison  with  the  laws  which  state 
the  connections  between  pressure,  temperature,  and  volume  in  the 
case  of  gases  (p.  n)  shows  that  the  laws  of  osmotic  pressure  are 
very  similar  ;  the  first  corresponds  to  Boyle's  Law,  the  second  to 
Charles's  Law,  and  the  third  to  Avogadro's  hypothesis.  In  order 
to  explain  this  remarkable  connection,  Van't  Hoff  has  suggested 
that  molecules  of  dissolved  solids  are  in  a  condition  similar  to 
those  of  gases,  and  can  therefore  exert  pressure  on  the  vessel 
which  contains  them,  as  gases  do,  the  solvent  having  little  or  no 
effect  upon  the  result.  This  explanation  is  generally  accepted. 


n6    A   FOUNDATION   COURSE   IN   CHEMISTRY 


Wattr 


To  understand  how  this  pressure  might  act,  imagine  a  glass 
cylinder  AC  (Fig.  15),  containing  sugar  solution  and  water,  with 
a  semi-permeable  partition  B  between,  as  shown  in  the  figure.  As 
the  molecules  of  sugar  exert  a  pressure  upon  the  under  surface  of 
the  partition,  they  will  tend  to  occupy  a  larger  volume  ;  but  as 
they  cannot  pass  through  the  partition,  the  only  way  in  which  the 
volume  can  increase  is  by  water  passing  through  into  the  sugar 
solution  ;  this  therefore  takes  place,  and  the  partition  moves  up 
the  cylinder.  An  experiment  of  this  nature  can 
actually  be  performed.  If  instead  of  a  sugar  solu- 
tion we  take  a  concentrated  solution  of  calcium 
nitrate,  saturated  with  phenol  (carbolic  acid),  and 
water  also  saturated  with  phenol,1  separated  by  a 
thin  layer — 2  or  3  mm  — of  phenol,  it  will  be  found 
that  this  layer  moves  up  the  cylinder  until  it  floats 
at  the  top.  The  phenol  acts  as  a  semi-permeable 
membrane,  water  passes  freely  through  it,  but  calcium 
nitrate  does  not.  The  passage  of  a  solvent  through 
a  membrane  which  is  impermeable  to  the  dissolved 
substance,  caused,  as  has  been  shown,  by  osmotic 
pressure,  is  called  osmosis. 

If  a  dissolved  substance  passes  freely  through  a 
membrane,  it  will,  of  course,  produce  no  osmotic 
pressure ;  and  when  substances  are  separated  by 
dialysis,  those  which  pass  through  the  membrane, 
are  those  which  exhibit  little  or  no  osmotic  pressure 
when  that  membrane  is  used.  The  measurement  of  the  osmotic 
pressure  of  colloid  solutions  could  be  carried  out  with  a  parchment 
membrane,  but  this  pressure  is,  in  the  case  of  such  substances, 
very  small  indeed,  owing  to  their  excessively  high  molecular 
weight. 

It  will  be  seen  that  osmotic  pressure  tends  to  attract  a  solvent 
into  the  solution,  and  to  retain  it,  and  it  therefore  exerts  a  resistance 
to  any  process  tending  to  remove  the  solvent.  For  this  reason  the 
boiling  point  of  a  liquid  is  raised  when  substances  are  dissolved 
in  it,  and  the  freezing  point  is  lowered. 


Sugar 
Solution 


FIG.  15. 


1  The  saturation  of  the  two  liquids  with  phenol,  is  to   prevent  the 
phenol  layer  from  dissolving. 


CHAPTER  XIII 

ORGANIC   MA1TER 

THE  chemical  compounds  which  enter  into  the  composition 
of  plants  and  animals  and  their  products,  e.g.  wood,  humus, 
fat,  flesh,  wool,  hair,  bones,  blood,  milk,  urine,  dung,  etc., 
differ  in  several  important  particulars  from  the  common  sub- 
stances previously  considered.  They  are  more  complex,  i.e. 
the  molecules  of  such  compounds  contain  a  larger  number  of 
atoms.  When  dried  and  heated  in  the  air,  they  burn.  The 
products  of  combustion  are  mainly  gases,  and  are  given  off. 
The  solid  substances  which  remain  are  called  ashes. 

The  combustible  part  is  often  called  organic  matter,  i.e. 
the  substance  or  product  of  an  organism.  The  ash  is,  by 
contrast,  often  referred  to  as  mineral  matter.  These  names 
are,  however,  apt  to  prove  misleading,  because  the  ash  is  just 
as  much  an  organic  product  as  the  combustible  matter.  The 
names,  however,  are  in  common  use  and  must  be  accepted. 

The  chemical  relation  of  the  constituents  of  the  ash — or 
some  of  them — to  the  compounds  of  which  the  combustible 
matter  is  made  up  is,  in  some  cases,  well  known;  in  others 
it  is  very  obscure. 

All  the  compounds  which  enter  into  the  composition  of 
the  combustible  matter  contain  the  elements  carbon  and 
hydrogen.  The  great  majority  also  contain  oxygen,  and  not 
a  few  contain  nitrogen  and  sulphur  as  well. 

When  the  substances  are  burned,  the  carbon,  hydrogen, 
and  sulphur  combine  with  oxygen,  forming  oxides.  Part 
of  the  oxygen  is  derived  from  the  substance  itself,  and 
the  remainder — the  larger  part— from  the  air  in  the  presence 
of  which  combustion  takes  place.  No  oxide  of  nitrogen  is 


u8    A   FOUNDATION   COURSE   IN   CHEMISTRY 

obtained,  as  nitrogen  does  not  combine  with  oxygen  at  the 
temperature  produced  by  the  combustion.  Nitrogen  is,  there- 
fore, liberated  in  the  free  state. 

Destructive  Distillation. — When  dry  organic  matter  is 
heated  in  closed  retorts  it  is  charred,  but  not  burned,  because 
the  air  has  no  access  to  it.  All  the  hydrogen,  oxygen,  and 
nitrogen,  most  of  the  sulphur  and  some  of  the  carbon  are 
expelled,  but  most  of  the  carbon  and  some  of  the  sulphur 
remain  in  the  retort.  The  elements  which  are  expelled  by 
heat  are  not  liberated  in  the  free  state,  but  as  volatile  com- 
pounds. These,  when  cooled,  separate  into  three  groups,  viz. 
(i)  tarry  matter,  (2)  substances  soluble  in  water,  and  (3) 
inflammable  gases.  The  exact  nature  of  each  of  these 
products  depends,  to  some  extent,  upon  the  temperature  and 
other  conditions  under  which  the  operation  is  performed, 
and,  in  larger  measure,  upon  the  nature  of  the  substance 
treated. 

When  wood  or  other  vegetable  matter  is  subjected  to 
destructive  distillation,  the  principal  volatile  products  are 
water,  acetone,  wood  spirit  and  pyroligneous  acid.  Wood 
spirit  is  one  of  the  inflammable  substances ;  it  consists  largely 
of  methyl  alcohol.  Pyroligneous  acid,  when  purified,  is  called 
acetic  acid.  The  sour  taste  of  vinegar  is  due  to  the  presence 
of  this  compound,  though  vinegar  is  manufactured  in  a  very 
different  way.  What  remains  in  the  retort  is  ordinary  wood- 
charcoal.  It  consists  of  the  free  element  carbon  mixed  with 
the  ash  ingredients  of  the  wood.  The  latter  can  be  separated 
by  treatment  with  dilute  acid,  and  pure  carbon  obtained.  In 
the  more  ancient  process  of  "  charcoal  burning,"  the  pieces  of 
wood  were  merely  stacked  on  the  ground,  covered  over  with 
turves  or  clay  to  prevent  free  access  of  air,  and  set  on  fire. 
The  heat  evolved  by  the  burning  of  part  of  the  wood  caused 
the  remaining  portion  to  be  subjected  to  dry  distillation,  but 
all  the  volatile  products  escaped  and  were  lost.1  These  volatile 
products  are  formed  by  the  destruction  of  certain  compounds 
during  the  process  of  distillation,  and  the  innumerable  minute 

1  This  process  is  still  carried  on  in  Sweden,  but  special  precautions  are 
taken  to  collect  the  tar,  which  is  sold  as  "wood-tar"  or  "Stockholm  tar." 


ORGANIC   MATTER  119 

spaces  which  the  compounds  occupied  in  the  original  sub- 
stance are  left  vacant.  Charcoal  is  therefore,  of  necessity, 
an  extremely  porous  substance,  and  has  a  large  internal 
surface.  When  gases  are  brought  into  contact  with  solid 
surfaces  they  become  denser  and  contract  in  volume;  they 
are  concentrated  as  a  denser  film  at  the  common  surface  of 
the  solid  and  gas.  All  porous  substances,  since  they  present 
a  large  extent  of  surface  in  small  space,  have,  therefore,  the 
power  of  absorbing  gases  in  their  vpores.  Charcoal  exhibits 
this  property  in  pre-eminent  degree.  That  made  from  the 
denser  kinds  of  wood  has  a  larger  number  of  smaller  pores, 
i.e.  a  greater  internal  surface,  and  can  absorb  larger  quantities 
of  gas.  Solid  and  liquid  substances  can  also  be  removed 
from  solution  in  water  by  charcoal  in  a  similar  manner. 

This  action  is  not  to  any  large  extent  due  to  oxidation 
by  any  oxygen  which  may  be  present  in  the  charcoal,  as  the 
efficiency  of  the  charcoal  is  greater  if  it  has  been  recently 
heated  so  as  to  expel  all  gas.  It  is  dependent  rather  upon  the 
fact  that  at  the  surface  of  contact  between  a  solid  body  and  a 
solution  the  dissolved  substance  becomesmore  concentrated  than 
in  the  remaining  part  of  the  solution.  Substances  of  complex 
composition  may  be  removed  from  solution  in  this  way.  The 
phenomenon  is  sometimes  known  as  adsorption.  It  is  because 
of  this  action  that  drinking-water  is  often  filtered  through 
charcoal.  Any  complex  organic  materials  present  are  adsorbed. 
Users  of  charcoal  filters,  however,  should  recognise  that  charcoal 
will  not  continue  to  remove  organic  matter  indefinitely,  and 
consequently  frequent  cleaning  of  the  filter  is  necessary. 

The  power  possessed  by  charcoal  of  absorbing  gases  can  be 
illustrated  by  filling  a  tube  with  ammonia  gas  over  mercury. 
If  a  piece  of  charcoal,  preferably  of  some  dense  wood,  and 
recently  heated,  be  introduced,  the  mercury  rises  quickly, 
showing  the  absorption  of  the  ammonia.  Some  kinds  of 
charcoal  absorb  ninety  times  their  own  volume  of  ammonia 
gas;  oxygen  is  absorbed  to  a  much  less  extent;  a  dense 
charcoal  only  absorbs  five  times  its  own  volume  of  this  gas. 

The  effect  upon  colouring  matter  in  solution  is  seen  on 
mixing  some  litmus  solution  with  powdered  charcoal  which 


120    A   FOUNDATION   COURSE   IN   CHEMISTRY 

has  been  freshly  heated.  On  filtering  the  mixture  the  liquid 
passes  through  the  filter  colourless. 

Charcoal  is  used  in  sugar  refining  for  the  purpose  of 
removing  traces  of  brown  resinous  colouring  material,  and 
so  giving  a  perfectly  white  sugar.1  It  has  also  the  power 
of  accelerating  catalytically  reactions  between  various  gases, 
but  in  this  respect  it  is  far  surpassed  in  efficiency  by  finely 
divided  platinum. 

Animal  matter,  such  as  bones,  hoofs,  horn,  hair,  wool, 
feathers,  etc.,  contains  a  much  larger  proportion  of  nitrogen 
than  wood  and  most  other  vegetable  products,  and  when  it 
is  subjected  to  destructive  distillation  most  of  the  nitrogen  is 
given  off  in  combination  with  hydrogen.  This  compound 
was  long  known  as  "  spirit  of  hartshorn,"  but  is  now  generally 
called  ammonia. 

Bone  charcoal  is  often  called  animal  charcoal,  but  the  latter 
term  properly  includes  charcoal  made  from  blood,  hides,  etc.2 

Coal. — Coal  is  often  spoken  of  as  a  mineral  because  it  is 
dug  out  of  the  ground.  In  reality,  it  is  derived  from  vegetable 
matter,  and  was  formed,  perhaps,  in  a  manner  similar  to  that 
in  which  peat  and  other  accumulations  of  a  like  nature  are 
being  formed  at  the  present  day.  Marked  differences  have 
been  observed  in  the  composition  of  the  upper  and  lower 
layers  of  peat  deposits.  The  latter  are  always  darker  in  colour 
and  denser.  They  contain  less  hydrogen,  oxygen,  and  nitrogen 
in  proportion  to  carbon.  It  is  by  further  changes  of  this  kind, 
and  strong  compression  due  to  the  enormous  weight  of  the 
superincumbent  rock  with  which  they  have  been  covered  up 
that  such  deposits  have  been  converted  into  coal.  Various 
"  intermediate  "  products  such  as  the  German  "  brown  coal  " 3 
are  known.  Similarly,  anthracite  or  "  stone  coal  "  represents 
a  further  stage  in  the  process  by  which  ordinary  soft  or 
household  coal  is  gradually  transformed  into  graphite. 

The  last-mentioned  substance  is  nearly  pure  carbon  ;  its 

1  The  whiteness  of  refined  sugar  is  generally  increased  by  the  addition 
of  minute  quantities  of  ultramarine. 

*  Bone  charcoal  is  the  material  used  in  sugar  refining. 

3  Known  also  as  lignite.  There  are  beds  of  it  at  Bovey  Tracey  in 
Devonshire. 


ORGANIC   MATTER  121 

formation  is  the  final  stage  of  the  process  by  which  all  the 
gaseous  elements  are  gradually  eliminated.  The  hydrogen 
and  oxygen  of  the  original  substance  appear  to  be  more 
rapidly  dispersed  than  the  nitrogen.  At  all  events,  ordinary 
coal  contains  less  hydrogen  and  oxygen  than  wood  does, 
while  the  nitrogen  content  is  about  the  same,1  or  slightly 
greater. 

Enormous  quantities  of  coal  are  subjected  to  destructive 
distillation  in  order  to  obtain  the  inflammable  gases  which  are 
used  for  illuminating  and  heating  purposes.  The  process  is 
carried  out  in  fire-clay  retorts,  which  somewhat  resemble  a  long 
drain  pipe  in  appearance.  The  form  of  carbon  which  remains 
is  called  coke.  Owing  chiefly  to  the  greater  density  of  the  coal, 
coke  differs  in  physical  properties  from  other  forms  of  charcoal. 
It  is  largely  used  for  burning  and  also  for  various  technical 
purposes,  such  as  iron  smelting. 

The  volatile  products 2  of  the  dry  distillation  of  coal  consist 
of  illuminating  gas  with  various  gaseous  impurities,  easily 
solidified  hydrocarbons  such  as  naphthalene,  coal  tar  and 
ammonia.  The  mixture  is  passed  through  a  cooling  apparatus 
to  condense  the  tarry  material,  and  water  in  which  the 
ammonia  dissolves.  The  illuminating  gas,  which  consists 
mainly  of  compounds  of  carbon  and  hydrogen,  is  insoluble 
in  water.  It  is  then  passed  over  quicklime  in  order  to  dry 

1  The  various  materials  mentioned  can  be  compared  in  the  following 
table,  which  gives  their  approximate  percentage  composition  : — 

Carbon.  Hydrogen.  Oxygen.  Nitrogen. 

Cellulose       50  6  43                      l 

Peat             60  6  32                    2 

Lignite          67  5  25                      2 

Soft  Coal      So  5  13 

90  5  4                     ' 

Anthracite     93  4  3 

2  Unpurified   coal   gas  would   probably   contain   the   following  con- 
stituents : — 

Sulphuretted  hydrogen      .     .    2     per  cent. 


Carbon  dioxide 2*5 

Unsaturated  hydrocarbons      .     3 
Carbon  monoxide    .     .     .     .     4' 5 

Hydrogen 47 

Saturated  hydrocarbons     .     .   38 
Nitrogen 3 


The  percentages 
are  subject  to  con- 
siderable varia- 
tions. 


122    A  FOUNDATION    COURSE   IN   CHEMISTRY 

it  and  to  remove  the  compounds  of  sulphur  which  it  contains. 
When  the  lime  is  slaked  and  so  contaminated  with  sulphur 
compounds  that  it  will  no  longer  act  as  a  purifier,  it  is  removed 
and  sold  as  "  gas  lime."  It  is  used  to  some  extent  by  farmers. 

The  tar  also  consists  mainly  of  compounds  of  carbon  and 
hydrogen,  and  yields  a  great  variety  of  useful  products,  such 
as  benzene,  carbolic  acid,  aniline,  creosote,  and  bitumen  or 
pitch. 

The  water  containing  the  ammonia  in  solution  is  called  the 
ammoniacal  liquor.  It  is  mixed  with  lime  and  distilled,  and 
the  ammonia  which  passes  over  is  made  to  combine  with 
sulphuric  acid  and  thus  form  sulphate  of  ammonia.  This 
substance  is  largely  used  as  a  nitrogenous  fertiliser,  and  it  is 
one  of  the  most  important  sources  of  other  ammonium 
compounds. 

Carbon. — The  element  carbon  is  an  essential  constituent 
of  every  kind  of  organic  matter.  In  most  cases  it  can  be 
obtained  by  destructive  distillation,  as  described  above.  The 
solid  black  residue  which  remains — wood  charcoal,  bone 
charcoal,  coke,  etc. — when  freed  from  ash  and  other  impuritie^, 
is  pure  carbon.  Fats,  tar,  and  many  other  carbon  compounds 
are  not  decomposed  on  heating,  but  in  many  cases,  if  burned 
in  a  limited  supply  of  air,  much  of  the  carbon  is  separated  as 
smoke,  which,  when  collected,  is  called  soot  or  lamp  black — 
the  latter  is  the  soot  from  burning  oil.  All  these  forms 
of  carbon  are  amorphous,  and  the  differences  in  their  physical 
properties  are  due  merely  to  the  accident  of  their  mechanical 
condition. 

Free  carbon  occurs  'in  nature  in  two  distinct  crystalline 
forms.1  The  commoner  of  these  is  the  familiar  substance 
graphite,  plumbago,  or  blacklead.  The  other  form  is  the 
diamond.  These  two  substances  differ  greatly  in  hardness, 
density,  behaviour  towards  light,  and  other  physical  properties. 
Graphite  is  black,  opaque,  and  so  soft  that  it  leaves  a  streak 
or  mark  when  lightly  rubbed  on  paper — hence  its  name  graphite.2 

1  Substances  occurring  in  two  crystalline  forms  are  said  to  be  dimorphic 
(two  formed). 

2  Gk.  ypdtyw,  I  write. 


ORGANIC   MATTER  123 

It  has  a  specific  gravity  of  2*21.  The  diamond  is  transparent, 
and  is  of  high  refractive  power  towards  light,  i.e.  rays  of  light 
entering  the  material  obliquely  are  bent  at  the  point  of  entry. 
It  is  the  hardest  of  all  known  substances,  and  it  is  therefore  used 
for  cutting  glass  and  for  cutting  and  polishing  other  diamonds.1 
It  has  a  specific  gravity  of  3*514. 

Amorphous  carbon  can  be  crystallised.  It  dissolves  in 
molten  iron,  silver,  and  other  metals,  and  when  these  solutions 
are  cooled  much  of  the  carbon  separates  in  the  crystalline 
form,  but  the  crystals  so  obtained  generally  resemble  graphite 
rather  than  diamond.  If,  however,  the  molten  iron  with  its 
dissolved  carbon  be  cooled  by  plunging  in  water,  the  outer  part 
of  the  mass  solidifies  and  contracts,  thus  subjecting  the  inner 
portion  to  immense  pressure  ;  under  these  conditions  the 
carbon  sometimes  crystallises  in  the  diamond  form,  but  the 
crystals  are  very  small. 

The  ultimate  identity  of  all  forms  of  carbon  is  established 
by  their  chemical  properties.  When  heated  in  oxygen  they 
all  combine  with  it  in  the  same  proportion  by  weight,  forming 
carbon  dioxide  (p.  68). 

When  carbon  dioxide  is  passed  over  red-hot  carbon  it  is 
reduced  — 


The  compound  produced  is  known  as  carbon  monoxide.  The 
equation  given  above  is  deduced  from  the  fact  that  when  the 
action  takes  place  the  volume  of  the  gas  is  doubled  —  that  is, 
every  volume  of  carbon  dioxide  produces  two  volumes  of 
carbon  monoxide,  and  therefore  every  molecule  of  carbon 
dioxide  gives  two  molecules  of  carbon  monoxide. 

The  reaction  takes  place  in  an  ordinary  coal  fire,  and  its 
effects  can  be  seen  when  all  the  hydrogen  and  other  gases 
have  been  driven  off  and  the  residue  of  the  coal  is  glowing. 
In  these  circumstances  air  enters  at  the  bottom  of  the  grate, 
and  the  coal  there  burns,  forming  carbon  dioxide.  This  gas 
in  passing  over  the  red-hot  coal  in  the  middle  and  upper  part 


1  The   word    "diamond"   is  from  the  Greek  oScfytas  (invincible),  of 
which  the  words  "adamant,"  "diamant,"  "diamond"  are  corruptions. 


i24    A   FOUNDATION   COURSE   IN  CHEMISTRY 

of  the  fire  becomes  reduced  to  carbon  monoxide,  which  burns 
on  passing  into  the  air,  with  a  blue  flame. 

Carbon  monoxide  is  also  produced  when  steam  is  passed 
over  red-hot  carbon.  This  is  done  in  most  gas-works,  glowing 
coke  being  employed.  The  gas  thus  formed,  is  a  mixture  of 
hydrogen  and  carbon  monoxide,  and  is  known  as  water  gas — 

H20-f-C-»CO  +  H2 

As  water  gas  has  no  illuminating  power  it  is  generally 
enriched  by  mixing  it  with  compounds  of  carbon  and 
hydrogen,  obtained  by  allowing  a  stream  of  high  boiling  rock- 
oil  to  fall  while  hot  upon  fire  brick. 

In  the  laboratory  carbon  monoxide  is  generally  prepared 
by  acting  on  certain  carbon  compounds  with  sulphuric  acid. 
The  most  convenient  is  formic  acid  H.COOH.  Concentrated 
sulphuric  acid  is  employed,  and  it  acts  as  a  dehydrator, 
removing  the  elements  of  water  but  not  otherwise  taking  part 
in  the  reaction  — 


JHJCOjOHj  -H2O-»CO 

Oxalic  acid  can  be  treated  in  the  same  way  with  similar 
results,  but  the  carbon  monoxide  obtained  is  mixed  with  an 
equal  volume  of  carbon  dioxide,  which  can  be  removed  by 
passing  through  caustic  potash. 


-H20-»C02  +  CO 
ICOjOHj 

The  gas  is  also  readily  prepared  by  heating  potassium 
ferrocyanide  with  concentrated  sulphuric  acid  — 

K4FeC6N6  +  6H2SO4  +  6H2O 

->  2K.SO,  +  3(NH4)2S04  4-  FeSO4  +  6CO 

Carbon  monoxide  is  a  colourless  gas,  very  slightly  lighter 
than  air,  insoluble  in  water,  and  neutral  to  litmus.  It  is 
intensely  poisonous  ;  it  forms  a  compound  with  the  red  colour- 
ing matter  of  the  blood,  which  is  difficult  to  decompose. 
Owing  to  the  readiness  with  which  it  combines  with  more 
oxygen,  it  is  a  powerful  reducing  agent  at  high  temperatures. 


ORGANIC   MATTER  125 

No  salts  corresponding  to  it  are  known,  and  it  cannot 
therefore  be  regarded  as  acidic,  but  it  forms  remarkable 
compounds,  known  as  carbonyls,  with  several  of  the  metals, 
potassium  (p.  97),  iron,  nickel,1  etc. 

It  also  combines  readily  with  an  equal  volume  of 
chlorine  gas  forming  carbonyl  chloride,  COC12  (phosgene  gas).2 

Carbonyl  chloride  reacts  with  ammonia — 


m      /iCl       H;NH2  /NH2 

C0<!      +  -»CO<  +2HC1 

NCI      H|NH2  XNH2 

The  compound  formed,  CO(NH2)2,  is  known  as  carbamide, 
or  urea ;  it  is  of  great  importance,  and  will  be  again  referred  to 
(p.  1 80). 

Ammonia. — The  principal  nitrogenous  compound  obtained 
by  the  dry  distillation  of  coal,  bones,  and  other  organic  material 
containing  nitrogen  is  called  ammonia.  It  is  a  colourless  gas, 
the  specific  gravity  of  which,  compared  with  air,  is  0*59 ; 
i.e.  it  is  much  less  dense  than  air.  It  has  a  strong  characteristic 
odour,  can  with  moderate  ease  be  condensed  to  the  liquid 
state,  and  is  readily  soluble  in  cold  water ;  one  volume  of  water 
dissolves  about  1150  volumes  of  ammonia  at  o°  C.  The 
whole  of  the  gas  may  be  expelled  from  the  solution  by  boiling. 
The  concentrated  solution  has  a  specific  gravity  of  o'88 
(water  =  i). 

The  composition  of  the  gas  corresponds  to  the  formula 
NH3.  This  is  best  proved  in  the  following  manner  : — 

A  long  tube  (Fig.  16),  closed  at  one  end  and  fitted  with  a 
tap  and  funnel  at  the  other,  is  filled  with  chlorine.  A  con- 
centrated solution  of  ammonia  is  then  allowed  to  run  into  the 
tube  drop  by  drop.  Vigorous  action  takes  place,  accompanied 
by  flashes  of  light.  When  chemical  action  has  ceased,  the 
whole  of  the  chlorine  will  have  disappeared,  and  if  water  be 
allowed  to  run  into  the  tube,  it  will  continue  to  do  so  until  it 
fills  two-thirds  of  the  length  of  the  tube.  The  gas  occupying 

1  Nickel  carbonyl,  Ni(CO)4,  forms  the  basis  of  a  method  for  purifying 
the  metal. 

2  Gk.  </>u>s,  light ;  ysvvaw,  I  produce. 


126    A   FOUNDATION   COURSE   IN    CHEMISTRY 


the  remaining  one-third  is  found  to  be  nitrogen,  which  must 
have  come   from  the  ammonia.      The  chlorine  removes  the 
hydrogen  from  the  ammonia,  forming  hydro- 
cloric  acid,  and  sets  the  nitrogen  free. 

3C1  4-  NH,  =  3HC1  +  N 

We  started  with  three  volumes  of  chlorine 
(the  tube  was  full)  and  finished  with  one 
volume  of  nitrogen.  But  three  volumes  of 
chlorine  will  combine  with  three  volumes  of 
hydrogen,  and  as  this  hydrogen  came  from 
the  ammonia  gas,  the  one  volume  of  nitrogen 
left,  must,  in  the  ammonia,  have  been  com- 
bined with  three  volumes  of  hydrogen. 

This,  however,  only  gives  the  proportion 
by  volume  in  which  the  two  gases  are  present, 
and  the  formula  might  be  not  only  NH3  but 
N2H6,  N3H9,  or  any  multiple  of  NH3,  for  the 
proportion  by  volume  would  be  the  same  in 
each  case. 

The  density  of  the  gas,  however,  is  8*5 
compared  with  hydrogen,  and  therefore  its 
molecular  weight  is  17  (p.  88).  The  atomic 
weight  of  nitrogen  is  14,  and  the  remainder,  3, 

is  equal  to  the  weight  of  3  atoms  of  hydrogen.     The  formula 

is  therefore  NH3. 

When  the  dry  gas  is  brought  into  contact  with  a  flame  it 

will  burn,  forming  water  and  liberating  nitrogen— 


FIG.  16. 


The  combustibility  of  ammonia  is,  however,  best  shown  by 
boiling  a  small  quantity  of  a  concentrated  solution  of  the  gas 
in  a  flask  (Fig.  17),  and  at  the  same  time  passing  in  oxygen 
by  means  of  a  glass  tube.  On  applying  a  light  to  the  mouth  of 
the  flask  the  ammonia  will  burn  with  a  yellow  flame,  and  will 
continue  burning  if  the  supply  of  oxygen  be  properly  adjusted. 

Liquid  anhydrous  ammonia  is  without  odour,  and  without 
action  on  litmus  paper ;  the  moist  gas,  however,  and  the  solution 
are  strongly  alkaline. 


ORGANIC   MATTER 


127 


When  mixed  with  dry  hydrochloric  acid  gas,  ammonia  gas 
forms  dense  white  fumes,  which  settle  on  the  sides  of  the  vessel 
as  a  fine  white  powder.  This  substance  is  called  ammonium 


*Oxygen  supply 


Strong  solution 
of  A  mmonia. 


FIG.  17. 

chloride,  and  is  produced   by  the   combination   of   the   two 
gases— 

NH3  +  HC1-»NH4C1 

Ammonium  chloride  was  the  first  known  compound  of 
ammonia,  and  was  called  "  Sal  ammoniac  "  *  (ammoniacal  salt), 
a  name  which  it  still  retains. 

When  ammonia  gas  dissolves  in  water  a  large  amount  of 
heat  is  evolved.     This  is  partly  due  to  the  immense  decrease 
in  volume  which  the  gas  undergoes,  and  to  a  small  extent  to 
actual  chemical  combination  with  the  water. 
NH3  +  H20  ->  NH4OH 

When  ammonia  is  driven  off  from  solution  a  like  amount 

1  On  the  ancient  trade  route  from  Berenice  (mod.  Ben  Ghazi)  to  the 
Nile  was  the  Temple  of  Jupiter  Ammon  (the  modern  name  for  the  place  is 
Siwah).  The  surrounding  oasis  was  a  popular  halting-place  for  caravans, 
and  the  chemical  changes  taking  place  in  the  immense  amount  of  organic 
refuse  which  accumulated,  led  to  the  formation  of  ammonium  chloride  as 
an  efflorescence  on  the  soil.  From  the  locality,  and  without  any  reference 
to  its  composition,  the  salt  was  called  "  Sal  ammoniac,"  and  when,  much 
later,  a  gas  was  obtained  from  it,  the  gas  was  called  ammonia. 


128     A  FOUNDATION    COURSE   IN  CHEMISTRY 

of  heat  must  be  absorbed.  This  may  be  shown  by  the 
following  experiment.  A  flask  about  half  full  of  strong 
ammonia  solution  is  placed  in  a  small  pool  of  water  on  a 
board.  Air  is  rapidly  drawn  through  this  solution  by  means 
of  a  filter  pump,  thereby  removing  the  ammonia  gas.  The 
liquid  is  rapidly  cooled,  and  ultimately  the  pool  of  water 
becomes  converted  into  ice.1 

That  ammonia  solution  contains  NH4OH,  ammonium 
hydroxide,  is  shown  by  its  action  upon  solutions  of  the  salts 
of  many  metals.  When,  for  instance,  it  is  added  to  a  solution 
of  ferric  chloride,  ferric  hydroxide  is  thrown  down — 

FeCl3  +  sNH4OH  ->  Fe(OH)3  +  sNH4Cl 

That  the  solution  also  contains  ammonia  gas  uncombined 
is  shown  by  another  action  which  often  takes  place. 

When,  for  example,  ammonia  solution  is  added  to  copper 
sulphate,  at  first  a  blue  precipitate  of  copper  hydroxide  is 
thrown  down — 

CuS04  +  2NH4OH  ->  Cu(OH)2  +  (NH4)2SO4 

but  further  addition  of  the  solution  of  ammonia  causes  the 
precipitate  to  dissolve  to  a  deep  blue  solution,  from  which  a 
dark  blue  crystalline  material  separates  out  on  addition  of 
alcohol.  This  compound  has  the  formula  CuSO4.4NH3.H2O. 

Many  similar  reactions  are  known.2  Because  of  its  action 
in  precipitating  hydroxides,  the  solution  of  ammonia  gas  is 
known  as  ammonium  hydroxide.  It  exhibits  the  characteristic 
odour  of  the  gas,  and  is  strongly  alkaline. 

It  can  be  neutralised  by  acids  which  act  upon  the  ammonium 
hydroxide  in  much  the  same  way  as  they  act  upon  caustic  soda 
or  any  other  soluble  hydroxide,  t.e.  they  form  water  and  the 
corresponding  salt — 

NH4OH  +  HNO,->  NH4NO,  +  H2O 
2NH4OH  +  H2SO4-»  (NH4)2SO4  +  2H2O 

NH4OH  +  HCl->  NH4C1  +  H2O 

1  Ammonia  gas  is  used  largely  in  the  manufacture  of  ice.  The  gas  is 
liquefied  by  pressure,  and  cooled.  It  is  then  allowed  to  freely  evaporate, 
when  great  absorption  of  heat  takes  place. 

8  Silver  chloride  is  soluble  in  ammonia  solution,  and  a  compound 
2AgC1.3NH3  can  be  separated. 


ORGANIC   MATTER  129 

These  reactions,  however,  may  be  looked  upon  as  direct 
unions  of  the  ammonia  with  the  acid,  thus — 

2NH3  +  H2SO4  ->  (NH4)2SO4,  etc. 

In  all  the  salts  formed,  the  group  NH4  occurs,  and  this  group 
plays  the  same  part  in  the  molecule  as  K  or  Na  in  the  corre- 
sponding potassium  or  sodium  compounds.  The  group  NH4, 
though  it  cannot  be  isolated,  is  called  the  radicle  (i.e.  root)  of 
the  compounds,  and  to  it  the  name  ammonium  has  been  given. 
The  metallic  suffix  "  um  "  does  not  here  suggest  that  ammonium 
is  a  metal,  but  rather  that  it  so  often  takes  that  place  in  a 
molecule  which  is  frequently  occupied  by  a  metal. 

Owing  to  the  fact  that  the  basic  radicle  of  the  compounds 
is  itself  complex,  ammonium  salts  are  decomposed  on  heating. 
If  the  acid  is  a  gas,  such  as  hydrochloric  acid,  it  is  volatilised 
along  with  the  ammonia,  and  the  two  recombine  on  cooling — 

NH4C1  ^  NH3  +  HC1 

As  the  products  of  the  decomposition  do  not  automatically 
separate,  but  remain  mixed  at  the  higher  temperature,  we 
generally  say  the  compound  is  dissociated.  It  is  owing  to  this 
dissociation  that  ammonium  chloride  is  volatilised  by  heat  and 
sublimes  on  cooling. 

If  the  acid  is  not  volatile,  the  products  of  decomposition 
do  not  remain  mixed  and  cannot,  therefore,  recombine  on 
cooling.  In  other  words,  the  ammonia  is  driven  off  and  the 
acid  remains — 

(NH4)2HPO4  ->  H3PO4  +  2NH3 

If  the  acid  is  an  oxidising  agent,  the  hydrogen  of  the 
ammonia  is  oxidised — 

(NH4)2Cr2O7    -»   Cr2O3  +  4H20  +  N2 

(Ammonium  bichromate.) 

NH4NO3      ->  2H2O  +  N2O     (Nitrous  oxide) 

(Ammonium  nitrate.) 

NH4NO2     ->  2H2O  +  N2 

(Ammonium  nitrite.) 

From  all  its  salts  ammonia  gas  is  displaced  by  the  action  of 
alkalies,  and  it  is  by  this  means  that  the  gas  is  usually  prepared— 
NH4C1  +  NaOH  -*»  Nad  +  H20  +  NH3 

K 


130     A    FOUNDATION   COURSE   IN   CHEMISTRY 

Instead  of  caustic  soda,  lime  or  other  basic  oxides  and 
hydrates  may  be  used — 

2NH4C1  +  CaO  ->  CaCl2  +  2NH3  +  H2O  1 

Similar  reactions  take  place  in  solution ;  the  ammonia  gas 
dissolves  in  the  water,  but  is  expelled  on  boiling,  and  can 
be  recognised  by  its  odour. 

Other  important  salts  of  ammonia,  besides  those  mentioned 
above,  are  the  carbonate  and  sulphide. 

The  carbonate  (NH4)2CO3  is  very  unstable  and  smells 
strongly  of  ammonia ;  the  bicarbonate  NH4HCO3  can  be  formed 
by  treating  ammonium  hydroxide  with  excess  of  carbon 
dioxide. 

Ammonium  "  sesquicarbonate  "  is  the  sublimate  obtained  by 
heating  a  mixture  of  ammonium  chloride  and  powdered  chalk 
(CaCO3).  It  is  a  mixture  of  bicarbonate  and  ammonium  car- 
bamate.  The  carbamate  is  also  formed  when  dry  ammonia 
and  dry  carbon  dioxide  are  mixed  together — 

2NH3  +  CO2  ->  NH4NH2CO2 

It  is  a  substance  closely  related  to  urea  (p.  180),  and  can 
be  represented  graphically — 

NH4  — Ox 

>C  =  O 

NH/ 

Ammonium  sulphide  is  used  in  chemical  analysis.  The 
solution  is  prepared  by  passing  sulphuretted  hydrogen  into 
ammonium  hydroxide,  and  contains  both  NH4HS  and 
(NH4)2S.  It  decomposes  on  keeping,  depositing  sulphur,  and 
becoming  yellow  from  the  formation  of  other  ammonium 
sulphides. 

Putrefaction  and  Decay. — When  organic  matter  putrifies, 
the  compounds  of  which  it  consists  are  gradually  broken  down 
and  various  compounds  of  hydrogen  are  produced.  The  simplest 
of  these  compounds  are  Marsh  gas  (CH4),  water,  sulphuretted 
hydrogen,  and  ammonia,  and  these  being  gases  are  given  off. 
It  will  be  seen  that  this  change  is  in  some  respects  analogous 

1  These  equations  suggest  the  use  of  ammonium  chloride,  but  of  course 
any  other  salt  of  ammonium  could  be  employed. 


ORGANIC   MATTER  13 1 

to  that  produced  by  destructive  distillation,  and  though  it 
takes  place  more  slowly,  the  products  are  to  some  extent  the 
same.  Putrefaction,  like  destructive  distillation,  can  only  take 
place  in  the  absence  of  air,  because,  in  both  cases,  the  products 
are  fairly  easily  oxidised,  and  therefore  would  not  otherwise  be 
obtained. 

In  the  presence  of  air,  destructive  distillation  gives  place 
to  combustion,  and  putrefaction  changes  to  decay,  which  is 
slow  oxidation.  The  final  products  of  decay  are  oxides  instead 
of  hydrides — 

C02,  H20,  S03,  N205. 

Both  putrefaction  and  decay  are  caused  by  bacteria,  and  a 
certain  degree  of  moisture  and  warmth  are  necessary  for  their 
action.  Within  certain  limits  the  greater  the  warmth  and 
amount  of  moisture  the  more  rapidly  do  the  bacteria  act  and 
the  more  rapidly  are  the  changes  accomplished. 

The  oxides  CO2,  SO3,  and  N2O5  are  all  acidic,  and  tend  to 
inhibit  the  action  of  the  bacteria  which  cause  decay.  The 
process,  therefore,  soon  comes  to  an  end  unless  lime  or  some 
other  basic  oxide  is  present  to  combine  with  these  products 
and  form  neutral  salts — carbonates,  sulphates,  and  nitrates. 

The  process  of  decay  takes  place  naturally  in  soils,  and  is 
called,  by  agricultural  chemists,  nitrification.  It  is  in  this  way 
that  the  organic  matter  of  the  soil^the  roots  of  previous 
crops  and  the  manure  applied  to  the  land — is  changed  into 
humus,  and  that  the  nitrogen  and  other  constituents  finally 
become  available  as  plant  foods.  In  soils  that  are  very  tightly 
packed  and  waterlogged,  nitrification  is  arrested  and  putrefac- 
tion set  up,  because  air  does  not  readily  find  access  to  such 
soils.  The  products  of  putrefaction  are  more  or  less  poisonous 
to  vegetation. 

The  process  of  nitrification  is  sometimes  promoted  by 
artificial  means.  For  this  purpose  the  organic  matter  is  mixed 
with  earth  and  lime  and  so  made  into  what  farmers  call  a 
compost.  The  heap  is  then  well  watered  with  liquid  manure, 
which  contains  plenty  of  bacteria,  and  covered  over  to  protect 
it  from  rain.  The  time  required  to  complete  the  change  depends 


132     A   FOUNDATION    COURSE   IN    CHEMISTRY 

largely  upon  the  temperature.  When  it  is  complete,  the 
material  is  carted  out  and  spread  upon  the  land. 

This  method  was  formerly  employed  for  the  production  of 
nitrates  which  were  used  for  making  gunpowder,  and  other  pur- 
poses. The  material,  instead  of  being  spread  on  the  land,  was 
lixiviated  with  water,  and  the  nitrates,  being  soluble,  dissolved. 
To  convert  the  calcium  nitrate  into  potassium  nitrate  (salt- 
petre) it  was  only  necessary  to  add  potassium  carbonate  to  the 
solution.  The  calcium  carbonate  produced  by  double  decom- 
position is  insoluble,  and  can  therefore  be  separated  by  filtra- 
tion. The  soluble  potassium  nitrate  can  be  obtained  from  the 
solution  by  crystallisation. 

Artificial  composts  are  not  now  required  for  the  production 
of  nitrates,  because  about  a  hundred  years  ago  large  deposits  of 
nitrate  of  soda  were  discovered  in  Chili.  This  in  its  crude 
form  is  known  as  caliche ;  it  was  probably  formed  from  organic 
matter  by  a  natural  process  of  nitrification,  and  the  deposits 
have  been  preserved  because  the  region  in  which  they  are 
found  is  practically  rainless. 

Fixation  of  Atmospheric  Nitrogen, — As  nitrogen  is  of  such 
great  importance  to  plants,  and  the  growth  of  grain  is  absolutely 
necessary  for  the  support  of  human  life,  various  attempts 
have  been  made  to  utilise  atmospheric  nitrogen,  which,  as  has 
been  already  stated,  plants  cannot  assimilate  while  it  is  in  the 
free  state  (p.  21).  Several  methods  are  now  in  use. 

It  was  shown  in  a  previous  chapter  (p.  21)  that  small 
quantities  of  oxide  of  nitrogen  are  formed  by  the  direct  com- 
bination of  oxygen  and  nitrogen  which  takes  place  under  the 
influence  of  electric  discharges.  It  has  long  been  known  that 
this  process  could  be  imitated  on  the  lecture  table.  With  the 
enormous  development  of  electrical  science  which  has  taken 
place  in  the  last  few  years,  it  has  been  found  possible  to  carry  it 
out  on  a  large  scale,  and  nitrates  are  now  commercially  manu- 
factured by  the  Birkland  and  Eyde  process  in  this  way. 
Instead  of  a  small  spark,  a  very  powerful  current  is  employed, 
and  the  gases  (i.e.  air)  are  passed  through  what  is  described  as 
"  a  roaring  disc  of  flame."  Under  these  conditions  the  oxygen 
and  nitrogen  combine  and  the  oxide  of  nitrogen  so  produced 


ORGANIC   MATTER  133 

is  brought  into  contact  with  lime   or   other   bases,  and   the 
corresponding  nitrates  are  formed. 

The  oxide  formed  when  oxygen  and  nitrogen  thus  unite 
is  nitrogen  peroxide,  which  in  contact  with  water  gives  nitric 
acid  and  nitric  oxide,  NO.  The  nitric  oxide  readily  takes 
up  further  oxygen,  forming  a  further  quantity  of  nitrogen 
peroxide. 

The  manufacture  of  nitrates  by  this  method  is  developing 
rapidly,  and  it  seems  probable  that  it  will  be  employed  not  only 
for  producing  nitrates  for  agriculture,  but  also  for  other  pur- 
poses. At  present  nitric  acid  and  the  compounds  derived 
from  it  are  chiefly  prepared  from  the  nitrate  of  soda  imported 
from  Chili. 

A  second  method  for  the  "fixation"  of  atmospheric 
nitrogen  also  depends  upon  the  application  of  electric 
energy.  When  nitrogen  is  passed  over  calcium  carbide  (p.  159) 
in  an  electric  furnace,  it  combines  with  the  carbide,  forming 
a  compound  known  as  calcium  cyanamide  Ca.C.N2 — or, 
Ca  =  N  —  C  =  N.  This  substance  is  also  used  as  a  nitro- 
genous fertiliser,  as  in  the  soil  the  nitrogen  it  contains  is 
converted  into  ammonium  carbonate  and  finally  into 
nitrate — 

CaCNa  +  4H20  +  CO2->  CaCO3  +  (NH4)2CO3 

The  following  are  also  important : — 

(i)  The  Production  of  Nitrides  of  Silicon  or  Magnesium.— 
When  magnesium  oxide  is  mixed  with  coal  or  coke,  heated 
in  an  electric  furnace  and  nitrogen  gas  is  passed  through  the 
mixture,  the  oxide  is  reduced  and  the  liberated  metal  unites 
with  the  nitrogen  forming  magnesium-nitride  (Mg3N2).  This 
substance  is  readily  acted  on  by  acids — even  carbonic  acid — 
with  the  formation  of  the  corresponding  ammonium  salt, 
thus — 

Mg3Na  +  7H80  +  C02-»  3Mg(OH)a  +  (NH4)2CO3 
Silicon  nitride  behaves  in  a  similar  manner.     These  com- 
pounds might  be  used  as  nitrogenous  manures ;  but,  though 
the  oxides  are  cheap  enough,  the  cost  of  manufacture  of  the 
nitrides  is  at  present  prohibitive. 


i34     A   FOUNDATION   COURSE   IN   CHEMISTRY 

(2)  The  Synthesis  of  Ammonia. — Air  and  steam  are  passed 
over  white  hot  coke  and  the  mixture  of  gases  thus  obtained 
(p.  24)  is  then  passed  over  wood  charcoal,  spongy  platinum 
or  other  catalyser.     They  are  then  mixed  with  more  steam 
and  again  passed  through  the  same  apparatus.     The  reactions 
which   take   place   may    be    represented    by    the    following 
equations — 

N2  +  3H2  +  2C02  +  2H2O  ->  2NH4HCO8 

(Ammonium  hydrogen  carbonate.) 

N2  +  3H2  +  2CO  -f  2H20->  2H.COONH4 

(Ammonium  formate.) 

Ammonium  formate  exhibits  a  tendency  to  decompose 
into  hydrocyanic  acid  and  water — 

H.COONH4->  HCN  +  2H2O 

Ammonia  is  formed  also  when  a  mixture  of  nitrogen  and 
hydrogen  is  passed  over  heated  metallic  calcium.  In  this 
case,  the  hydride  CaH2  is  first  formed  and  ammonia  is 
ultimately  produced  from  it  by  the  reactions  expressed  in  the 
following  equations — 

Ca-f  H2-»CaH.2 
3CaH2  +  2Na-»  Ca,Na 
Ca,N,  -I-  6H2  ->  3CaHa 

Nitrogen  combines  directly  with  hydrogen  to  a  certain 
extent  when  an  electric  spark  is  passed  through  a  mixture 
of  the  gases. 

(3)  Formation  of  Cyanides. — When  a  mixture  of  carbon 
and   potassium   carbonate  is   heated   to   bright   redness   and 
nitrogen  gas  (air)  is  led  over  the  glowing  mass,  the  nitrogen 
enters  into  combination  and  forms  potassium  cyanide  KCN. 
This  is  one  of  the  oldest,  and  until  comparatively  recent  years, 
it  was  almost  the  only  known  method  of  causing  the  free 
element  nitrogen  to  enter  into  combination. 

Nitric  Acid.— When  nitrate  of  soda,  or  any  other  nitrate, 
is  heated  with  concentrated  sulphuric  acid,  nitric  acid  distils 
over.  This  change  may  be  represented  by  the  equation— 

NaNO3  +  H2SO4  =  NaHSO4  -f  HNO3 


ORGANIC   MATTER  135 

It  has  been  argued  from  this  that  sulphuric  acid  is  the 
stronger  acid,  i.e.  that  it  has  a  greater  affinity  for  bases  than 
nitric  acid.  The  inference,  however,  is  not  strictly  accurate. 
More  heat  is  evolved  in  the  formation  of  nitrates  than  in  the 
formation  of  the  corresponding  sulphates,  and  that  is  a  more 
accurate  measure  of  chemical  affinity.1 

The  action  of  sulphuric  acid  on  nitrates  does  not  proceed 
very  fast  or  very  far  unless  the  nitric  acid  is  removed  (by  dis- 
tillation) as  it  is  produced.  Otherwise,  there  is  a  tendency  for 
the  reverse  change  to  take  place,  and  a  condition  of  equilibrium, 
which  is  determined  by  the  relative  masses  of  the  reacting 
bodies,  is  set  up. 

Nitric  acid  is  a  liquid,  sp.gr.  1*53.  When  pure  it  is 
colourless,  and  has  a  strong  characteristic  odour.  Generally 
nitric  acid  is  coloured  yellow  by  the  presence  of  nitrogen 
peroxide. 

The  composition  of  nitric  acid  is  indicated  by  the  formula 
HNO3.  As  the  name  of  the  substance  implies,  it  has  strongly 
acid  properties  ;  it  turns  blue  litmus  red,  decomposes  carbonates, 
and  combines  with  basic  oxides  to  form  well-defined  salts 
(nitrates). 

In  concentrated  solution  it  is  an  oxidiser,  and,  with  certain 
organic  compounds,  it  forms  nitro-compounds,  i.e.  it  introduces, 
into  these  compounds  the  group  NO2,  most  of  which  are  yellow 
in  colour.  For  this  latter  reason  it  stains  the  skin  yellow. 

Its  oxidising  power  is  well  seen  in  its  action  upon  carbon 
which  is  caused  to  deflagrate,  and  also  upon  tin  — 

Sn  +  4HNO3  ->SnO2  -f  4NO2  +  2H2O 


As  the  equation  shows,  the  acid  is  itself  reduced. 

It  is  easy  to  understand  this  and  other  similar  reactions  if 
we  remember  that  nitric  acid  is  a  hydrate,  i.e.  a  compound  of 
N2O5  with  water  — 

N2O5  +  H2O  ->  2HNO3 

1  Moreover,  when  equivalent  quantities  of  NaOH.HNO3  and  H2SO4 
mutually  react  in  dilute  aqueous  solution,  two-thirds  of  the  soda  com- 
bines with  the  nitric  acid  and  one-third  with  the  sulphuric  acid.  Nitric 
acid  in  aqueous  solution  is  therefore  a  "  stronger  "  acid  than  sulphuric 
acid. 


136     A   FOUNDATION   COURSE   IN   CHEMISTRY 

The  formula  for  nitric  acid  can  be  written  HO.NO2,  and 
the  change  which  takes  place  in  it  when  it  acts  upon  tin  can  be 
indicated  as  follows  :  — 


HO  ! 

i  N02 

......! 

: 

HJO 

|  N02 

When  nitric  acid  acts  upon  copper,  the  change  which  takes 
place  depends  upon  the  strength  of  the  acid  employed.  With 
a  somewhat  diluted  acid  nitric  oxide  is  produced — 

3Cu  +  8HN03->  4H20  +  sCu(N03)2  -f  2NO 

But  if  concentrated  acid  be  employed,  nitrogen  peroxide 
is  obtained — 

Cu  +  4HNO3->  2H2O  +  Cu(NO3)2  +  2NO2 

The  fact  that  the  acid  is  acting  as  an  oxidising  agent  is 
seen  from  the  liberation  of  oxides  of  nitrogen,  which  in  each 
case  contain  less  oxygen  than  is  present  in  the  nitric  acid,  i.e. 
less  than  in  N2O5. 

Nitric  acid  acts  upon  silver,  lead,  and  other  metals  in  a 
similar  manner.  Dilute  nitric  acid  has  less  effect  upon  these 
metals,  but  upon  zinc,  iron,  and  other  easily  oxidisable  metals 
it  acts  vigorously,  forming  nitrates  and  liberating  oxides  of 
nitrogen,  nitrogen,  or  ammonia.  The  nature  of  the  products 
depends  upon  the  temperature  and  concentration  of  the  acid. 

With  very  dilute  nitric  acid,  magnesium  causes  the  evolution 
of  hydrogen;  a  fact  which  is  of  some  importance  as  it 
emphasises  the  acidic  properties  of  nitric  acid  when  it  is 
made  very  dilute. 

All  nitrates  are  soluble  in  water.  When  heated  strongly 
in  the  dry  state  they  undergo  decomposition. 

The  nitrates  of  the  alkali  metals  (p.  193)  lose  oxygen  on 
being  heated — 

KNO3  ->  KNO2  +  O 

(Potassium  nitrite.) 

The  nitrates  of  the  heavy  metals  lose  oxygen  and  nitrogen 
peroxide,  and  leave  an  oxide — 

Pb(NO3)a-»  PbO  +  2NO3  +  O 


ORGANIC   MATTER  137 

If  the  oxide  is  unstable  the  metal  itself  will  be  left — 

AgN03->Ag  +  N02  +  0 

Nitric  acid  (hydrogen  nitrate)  behaves  like  the  nitrates  of 
the  heavy  metals,  i.e.  it  is  split  up  into  the  oxide  (H2O),  NO2 
and  oxygen  which  may  be  collected. 

Nitrate  of  ammonia  decomposes  completely  (p.  129). 

The  Oxides  of  Nitrogen.— (i)  Nitrous  Oxide,  N2O  formed 
by  the  decomposition  of  ammonium  nitrate.  It  is  a  colourless 
gas,  slightly  soluble  in  cold  water,  neutral  to  litmus.  When 
inhaled  it  produces  in  some  people  a  form  of  hysteria,  and 
is  therefore  called  cc  laughing  gas."  If,  however,  it  is  breathed 
in  a  pure  state  it  produces  insensibility,  and  is  therefore  used 
by  dentists  as  an  anaesthetic.  Combustible  bodies  such  as 
sulphur  will  burn  in  it,  combining  with  the  oxygen  and  liberating 
nitrogen. 

(2)  Nitric  Oxide  NO. — Generally  prepared  by  the  action 
of  slightly  diluted  nitric  acid  upon  copper  (p.  206).      It  is  a 
colourless   gas    insoluble   in   water,  and   neutral   to    litmus. 
It    rapidly    takes    up    oxygen,   forming    nitrogen    peroxide. 
It  supports  combustion  in  the   same   way  as   nitrous   oxide 
does. 

(3)  Nitrogen  trioxide,    N2O3.— The   reduction   product   of 
nitric  acid  formed  when  that  acid  is  acted  upon  by  starch  or 
white  arsenic  As4O6.     When  condensed  it  forms  a  deep  blue 
liquid.     In  the  gaseous  state  it  is  almost  entirely  dissociated 
into  NO  and  NO2. 

N2O3  is  the  anhydride  of  nitrous  acid  HNO2,  the  salts  of 
which  are  known  as. nitrites.  The  formation  of  potassium 
nitrite  from  the  nitrate  has  already  been  mentioned. 

Both  nitrates  and  nitrites  are  sometimes  found  in  natural 
waters,  particularly  surface  water.  Any  water  containing 
appreciable  amounts  of  these  compounds  should,  if  it  is  to 
be  used  for  domestic  purposes,  be  viewed  with  suspicion ; 
not  because  the  nitrates  and  nitrites  are  themselves  dangerous, 
but  because  they  are  formed,  as  has  been  shown,  by  the 
oxidation  of  organic  matter  almost  always  of  animal  origin. 
Organic  matter  may  therefore  be  present  in  the  water,  and 


138     A   FOUNDATION   COURSE   IN   CHEMISTRY 

this  may  possibly  be  accompanied  by  bacteria  of  putrefaction 
and  disease. 

(4)  Nitrogen  peroxide,  NO2,  the  brown  oxide  of  nitrogen, 
is  soluble  in  water,  with  which  it  forms  nitric  acid  and  nitrous 
acid  or  nitric  oxide. 

(5)  Nitrogen  pentoxide,  N2O5,  the  anhydride  of  nitric  acid. 
It  can  be  obtained  from  the  acid  by  treatment  with  phosphorus 
pentoxide,  P2O5— 

2HN03  +  P205->  N205  +  2HP03 

It  is  a  white  solid  very  readily  soluble  in  water.  It  speedily 
decomposes  into  nitrogen  peroxide  and  oxygen  with  evolution 
of  heat. 


CHAPTER   XIV 

PARAFFINS   AND   THEIR   DERIVATIVES 

DURING  the  putrefaction  of  vegetable  material  in  the  presence 
of  moisture  various  gaseous  products  are  evolved.  One  of 
these  is  particularly  noticeable  as  coming  off  in  bubbles  from 
the  vegetable  refuse  which  collects  at  the  bottom  of  stagnant 
pools.  If  a  glass  jar  be  filled  with  water  and  inverted  with 
the  mouth  below  the  surface  of  the  pool  and  the  mud  below 
it  stirred,  it  is  possible  to  collect  the  gas  in  the  jar. 

Owing  to  its  formation  in  the  circumstances  described,  the 
gas  is  known  as  Marsh  gas.  If  a  lighted  match  be  applied  to 
the  gas  it  will  burn,  forming  carbon  dioxide  and  water. 

Marsh  gas  is  also  formed  during  the  destructive  distillation 
of  organic  matter  and  constitutes  a  large  percentage  of  gas 
coal.  It  is  also  given  off  from  coal  in  the  mine,  and  is  the 
"  fire  damp  "  of  the  coal-miner. 

For  experimental  purposes  marsh  gas  is  generally  prepared 
by  heating  dry  sodium  acetate  with  caustic  soda  or  soda  lime — 

CH3COONa  +  NaOH  ->  CH4  +  Na2CO3 

It  is  colourless,  tasteless,  odourless,  and  practically  insoluble  in 
water. 

Analysis  of  the  gas  shows  that  it  consists  of  carbon  and 
hydrogen  only,  and  its  percentage  composition  and  its  density 
(eight  compared  with  hydrogen)  lead  to  the  formula  CH4. 
In  its  general  properties  it  closely  resembles  a  large  series  of 
compounds  of  hydrogen  and  carbon  which  are  known  as  the 
paraffins,  and  which  are  found  in  petroleum  or  rock  oil. 
Many  of  these  compounds  are  in  general  use  as  fuels  under 
the  names  of  paraffin  oil,  etc. 


140    A   FOUNDATION   COURSE   IN   CHEMISTRY 

Ordinary  paraffin  oil  is  a  familiar  substance  easily  recognis- 
able by  its  peculiar  characteristic  odour.  It  is  a  liquid,  lighter 
than  water  and  insoluble  in  it.  It  takes  fire  readily  and  burns 
with  a  brightly  luminous  flame. 

It  is  obtained  from  the  crude  petroleum,1  which  springs 
from  the  earth  in  certain  places  on  the  shores  of  the  Caspian 
Sea,  in  the  United  States  of  America  and  Canada.  A  similar 
material  is  obtained  by  destructive  distillation  of  bituminous 
shales  in  Scotland. 

All  these  products  consist  not  of  a  single  pure  substance, 
but  of  a  mixture  of  many  which  can  be  separated  more  or  less 
completely  by  processes  of  distillation. 

The  crude  petroleum  contains  marsh  gas  and  other 
substances,  gaseous  at  the  ordinary  temperature,  but  these 
are  largely  given  off  on  exposure  to  the  air.  On  distillation 
it  is  found  that  the  petroleum  has  no  definite  boiling  point, 
but  that  the  temperature  of  ebullition  gradually  rises,  and 
condensable  vapours  are  given  off  at  all  temperatures.  The 
most  volatile  products  come  over  first,  the  liquid  commencing 
to  boil  at  about  38°  C.,  and  the  distillate  which  is  condensed 
between  this  temperature  and  about  100°  C.  constitutes  the 
extremely  volatile  material  known  as  "  petrol "  or  "  motor 
spirit."  When  this  is  removed,  liquids  of  higher  boiling  point 
are  given  off  and  condensed ;  these  form  the  material  known 
by  various  names  such  as  benzoline,  gasoline,  etc.  On  con- 
tinuing the  heating,  further  products  are  obtained,  most  of 
which  are  used  as  lamp  oils,  and  after  these  have  been  collected, 
further  separation  yields  lubricating  oils,  vaseline,  and  solid 
paraffin  (paraffin  wax). 

By  careful  redistillation,  each  of  the  liquid  products  can 
be  separated  into  a  number  of  more  or  less  pure  substances, 
but  it  is  impossible  by  mere  distillation  to  obtain  each  con- 
stituent compound  in  petroleum  in  a  perfectly  pure  condition. 

By  special  treatment,  however,  a  liquid  can  be  obtained 
with  a  constant  boiling  point  of  38°  C.,  another  with  a  constant 

1  Crude  petroleum  often  contains  sulphur  compounds.  These  give  an 
objectionable  odour  to  the  oil  itself,  and  produce  sulphur  dioxide  on 
burning.  They  are  removed  by  heating  the  oil  with  copper  oxide,  CuO. 


PARAFFINS   AND   THEIR   DERIVATIVES      141 

boiling  point  of  70°  C.;  a  third  which  boils  at  98°  C.,  and  others 
which  boil  at  125°  C.,  148°  C.,  etc.  Analysis  and  general  study 
of  these  compounds  have  caused  the  formulae :  C5H12,  C6H14, 
C7H16,  C8H]8,  CgHso  to  be  assigned  to  them  respectively.  Others 
which  are  gaseous  at  ordinary  temperatures  are  represented 
by  the  formulae  :  C2H6,  C3H8,  C4H10. 

It  is  obvious  that  a  close  relationship  exists  between  these 
compounds.  They  are  all  hydrocarbons  (i.e.  compounds  of 
hydrogen  and  carbon  only),  and,  commencing  with  marsh  gas 
CH4,  there  is  a  complete  series  in  which  each  member  differs 
by  one  carbon  atom  and  two  hydrogen  atoms  from  that 
immediately  preceding  it.  In  each  case  also  the  number  of 
hydrogen  atoms  is  just  two  more  than  twice  the  number  of 
carbon  atoms.  To  express  this  fact  a  general  formula  (i.e.  one 
which  applies  to  each  compound)  is  used,  it  is  QH^  +  2- 
Here  if  "^"  is  i,  then  2n  +  2  ==  4,  and  the  hydrocarbon 
is  CH4.  If  "»"  is  6  then  2n  -f  2  =  14,  and  the  hydrocarbon 
is  C6H14. 

A  series  in  which  the  members  differ  by  a  constant 
quantity  is  called  a  homologous  series.  The  series  now 
being  considered  is  that  of  the  paraffin  hydrocarbons.  Other 
homologous  series  are  known. 

A  special  nomenclature  has  been  adopted  for  these  com- 
pounds, and  names  given  to  them  which,  in  most  instances, 
indicate  by  the  use  of  a  Greek  numeral  the  number  of  carbon 
atoms  in  the  molecule,  and  which  terminate  in  the  syllable 
"  ane." 

Thus— 

CH4  is  Methane.  C6H14  is  Hexane. 

C2H6  „  Ethane.  C7H16  „  Heptane. 

C3H8  „  Propane.  C8H18  „  Octane. 

C4H10  „  Butane.  C9H2o  „  Nonane. 

C5H12  „  Pentene.  QoH^  „  Decane. 

(This  marks  the  commencement  of  the  CnH24  „  Undecane. 

use  of  the  Greek  numeral  prefix.)  C^H^  „  Dodecane, 

etc.,  etc. 

The  first  four  members  of  the  series  are  gases  at  ordinary 


142     A    FOUNDATION    COURSE   IN   CHEMISTRY 

temperatures,  the  succeeding  members  from  pentane  to  hecde- 
cane  C16H34  are  liquids,  and  the  remainder  solids.  It  will  be 
seen  that  as  the  molecule  increases  in  complexity l  the  higher 
the  boiling  point  becomes,  although  there  is  not  a  regular 
difference  between  the  boiling  points  of  successive  members 
of  the  series.  The  difference  is  less  in  the  case  of  the  higher 
members  of  the  series  than  in  the  case  of  the  lower. 

Thus  Pentane  C5H12  boils  at  38°  C,  and  Hexane  at  70°  C., 
a  difference  of  32°  C. ;  Octane  boils  at  125°  C.,  Nonane  at 
148°  C.,  a  difference  of  23°  C. 

In  chemical  behaviour,  the  paraffin  hydrocarbons  are 
singularly  inert;  neither  caustic  soda,  sulphuric  acid,  nor 
hydrochloric  acid  have  any  effect  upon  them.  The  name 
"  paraffin  "  is  intended  to  emphasise  this  point.2 

Fuels. — Perhaps  the  most  important  application  of  the 
paraffins  is  'as  fuel.  All  fuels  contain  either  hydrogen  or 
carbon,  or  both,  and  their  use  depends  upon  the  fact  that  these 
elements  when  combining  with  oxygen  give  out  large  amounts 
of  heat. 

Occasionally  alcohol  is  used  as  a  fuel,  but  this  is  not  so 
effective  as  an  equal  weight  of  a  hydrocarbon,  since  it  already 
contains  oxygen  as  well  as  hydrogen  and  carbon,  and  therefore 
less  oxygen  is  necessary  to  convert  it  into  carbon  dioxide  and 
water,  and  less  energy  in  the  form  of  heat  is  liberated.  The  use 
of  liquid  fuel  is  rapidly  extending  owing  to  its  portability, 
cleanliness,  and  convenience  in  use. 

Lamp  Oils. — Oils  for  use  in  lamps  should  be  free  from  the 
more  volatile  paraffins,  as  otherwise  they  will  give  off  an 
inflammable  vapour  at  ordinary  temperatures.  The  tempera- 
ture at  which  an  oil  gives  off  an  inflammable  vapour  is  called 
its  flash-point.  In  Great  Britain  no  oil,  the  flash-point  of 
which  is  below  73°F.,  can  be  sold  as  lamp  oil.  This  is 
somewhat  low,  but  nearly  all  specimens  of  lamp  oil  on  sale  in 
the  country  will  be  found  to  have  their  flash-points  considerably 
higher. 

1  This  statement  applies  strictly  to  the  normal  members  of  the  series 
only.  An  important  qualification  will  be  found  in  more  advanced  works 
on  organic  chemistry. 

*  Lat,  famm,  a/tttis,  lit.  little  affinity. 


PARAFFINS   AND   THEIR   DERIVATIVES      143 

Lubricating  Oils. — The  use  of  some  of  the  less  volatile 
paraffins  as  lubricants  depends  upon  the  fact  that  they  do  not 
dry,  and  do  not  oxidise  in  the  air;  there  is,  therefore,  no 
chance  of  their  forming  any  acid  substances  which  might 
corrode  metal,  or  resinous  material  which  might  increase 
friction. 

Vaseline. — This  substance  is  also  used  as  a  lubricant.  Its 
use  in  medicine  arises  from  its  being  neither  acid  nor  alkaline, 
from  its  permanency,  in  that  it  does  not  decompose  or  in  any 
way  change  on  keeping ;  also  from  its  having  the  usual  inert 
character  of  the  paraffins,  and  not  reacting  with  any  of  the 
medicaments  with  which  it  may  be  mixed. 

Paraffin  Wax. — This  substance  is  soluble  in  paraffin  oil, 
and  in  benzene,  and  solutions  in  one  or  other  of  these 
solvents  are  used  for  waterproofing  leather  (boots,  etc.).  A 
solution  in  turpentine  is  occasionally  rubbed  into  wood  to 
form  a  temporary  protection  against  water  and  acids. 

Paraffin  wax  is  also  largely  used  in  the  manufacture  of 
candles.  It  occurs  as  a  solid  mineral  occasionally,  when  it  is 
known  as  "  ozokerite." 

Constitution. — As  methane  is  correctly  represented  by 
the  formula  CH4,  it  is  evident  the  carbdn  in  it  is  tetra- 
valent.  By  no  known  process  can  carbon  be  made  to 
combine  with  more  than  four  atoms  of  hydrogen  or  their 
equivalent,  and  therefore,  before  any  other  compound  can 
be  formed  from  methane,  some  of  the  hydrogen  must  be 
removed. 

For  instance,  two  molecules  of  methane  cannot  unite,  but 
if  one  atom  of  hydrogen  were  removed  from  each,  leaving 
CH3,  these  residues  might  combine  together.  This  can  be 
represented  graphically.  Methane,  for  example,  can  be 
written — 

H 

H— C— H 


i 


The/wr  lines  radiating  from  the  carbon  atom  merely  signify 


144     A   FOUNDATION    COURSE    IN    CHEMISTRY 

that  carbon  is  tetravalent.     The  residue,  CH3,  will  then  be 
represented  as — 

H 

H— C— 


and  two  of  these  may  readily  join  together — 

H     H 

H— C— C— H 

I       I 
H     H 

forming  a  molecule  of  C2H6.  It  is  plain  that  in  this  molecule 
the  two  carbon  atoms  must  be  directly  united.  This  process 
might  be  repeated  indefinitely,  so  that  from  C2H6  a  hydrogen 
atom  might  be  removed  and  another  CH3'  added  in  its  place, 
forming — 

H    H    H 

I       I       I 
H— C— C— C— H 

L    I     I 

H    H    H 

*>.  C8H8,  and  so  the  next  compound  C4H10,  being  CH3 — CH2 
— CH3 — CH2. 

As  a  matter  of  fact  this  kind  of  formula  does  completely 
represent  the  paraffin  hydrocarbons,  and  is  in  general  use. 
The  formulae  show  diagrammatically  the  following  charac- 
teristics of  the  paraffins. 

(a)  The  number  of  hydrogen  atoms  is  just  two  more  than 

twice  the  number  of  carbon  atoms. 
(If)  Each  member  of  the  series  differs  by  CH2  from  that 

immediately  preceding  it. 

(c)  Every  atom  of  carbon  is  exercising  its  full  combining 
power,  and  therefore  no  other  compounds  can  be 
formed  from  the  paraffins  except  by  removal  of 
hydrogen.1 

1  It  must  be  carefully  noted  that  we  do  not  assume  the  formulae  and 
deduce  the  properties  of  the  paraffins  from  them.  The  formulae  are  used 
as  diagrammatic  representations  of  facts  obtained  by  experiment, 


PARAFFINS   AND   THEIR   DERIVATIVES      145 

Compounds  which  exhibit  this  last  property  of  forming 
other  compounds  only  when  certain  of  the  elements  they 
already  contain  are  removed,  are  called  saturated  compounds, 
and  the  derivative  compounds  are  said  to  be  formed  by 
substitution. 

The  paraffins  are  saturated  hydrocarbons,  for  we  find  that 
only  substitution  compounds  can  be  formed  from  them.  As  a 
simple  example,  consider  what  takes  place  when  methane  is 
mixed  with  chlorine.  When  the  mixed  gases  are  exposed  to 
the  action  of  sunlight,  part  of  the  chlorine  enters  into  the 
methane  molecule,  in  place  of  hydrogen,  which  is  removed  in 
combination  with  the  rest  of  the  chlorine.  Thus, 

CH4  +  Cl2->CH3Cl-f  HC1 

This,  however,  may  proceed  further,  until  all  the  hydrogen 
has  been  replaced  by  chlorine  — 

CH3C1  +  Cla->  CH2C12  +  HC1 
CH2C12  +  Cla  ->  CHC13*  +  HC1 
CHCl3-r-Cla->CCl4t  +HC1 

These  compounds,  in'  which  atoms  of  hydrogen  are  replaced 
by  atoms  of  chlorine,  are  known  as  chlor-substitution  products. 
It  would  be  difficult  to  obtain  the  pure  compounds  by  the 
method  suggested. 

Similar  compounds  can  be  derived  from  other  paraffins, 
and  we  have  thus  three  homologous  series  of  such  derivatives 
(omitting  those  in  which  the  whole  of  the  hydrogen  is  replaced), 
viz.  the  monochlor-substitution  products  of  the  general  formula 
CHH2n+iCl;  the  dichlor-substitution  products  of  the  general 
formula  CnH2MCl2  and  the  trichlor-substitution  products, 


When  one  hydrogen  atom  of  methane  is  replaced  by  any 
other  element,  the  group  CH3  will  be  found  in  the  substitution 
product.  This  group  is  referred  to  as  methyl.  Similarly,  in 
the  mono-substitution  products  of  ethane,  the  group  C2H5  will 

*  CHC13  is  the  compound  known  as  chloroform. 

t  CC14,  Carbon  tetrachloride.  A  volatile,  inflammable  liquid  ;  both 
it  and  chloroform  have  well-marked  anaesthetic  properties. 


146     A   FOUNDATION   COURSE   IN   CHEMISTRY 

be  found ;  this  is  known  as  ethyl ;  C3H7  is  propyl,  C4H9~  is 
butyl,  and  so  on. 

The  compounds  derived  from  ethane  by  substitution  of  the 
hydrogen  by  chlorine  are  C2H5C1,  C2H4CL,  C2H3C13,  etc.  The 
first  of  these,  C2H6C1,  may  be  called  monochlorethane.  It  is, 
however,  often  referred  to  as  ethyl  chloride.  It  is  a  volatile 
liquid.  It  reacts,  under  proper  conditions,  with  moist  silver 
oxide,  forming  silver  chloride,  and  a  hydroxyl  derivative  of 
ethane,  which  we  may  call  ethyl  hydroxide — 

C2H9C1  4-  AgOH  ->  AgCl  +  QH8OH  l 
Ethyl  hydroxide  can  be  represented  thus— 

H    H 
H— C— C— O— H 


The  formula  shows  diagrammatically  that  the  chlorine  has 
now  been  replaced  by  hydroxyl2  (OH).  Oxygen  is  a  dyad 
element,  and  therefore  the  group  OH  is  capable  of  combining 
with  one  more  atom  of  hydrogen  or  any  other  monad  element, 
or  with  one  monad  group,  such  as  ethyl. 

The  two  atoms  of  chlorine  in  dichlorethane  C2H4C12  may 
be  replaced  by  one  atom  of  oxygen,  giving— 

H     H 

I       I 
H—  C—  C  =  O    U  CH3CHO 


I  n  the  case  of  trichlorethane,  both  replacements  are  possible, 
i.e.  one  atom  of  chlorine  by  hydroxyl,  and  the  other  two  atoms 

1  The  corresponding  iodine  compound  C2H5I  being  less  volatile  is  much 
more  convenient  for  this  substitution. 

2  Whenever   the  group  OH   occurs  in   combination  it  is  known  as 
hydroxyl.      It   cannot,    of    course,    be    obtained    free,    any    more    than 
methyl  or  ethyl.     These  and  others  are  complex  radicles  occurring  only  in 
combination. 


PARAFFINS   AND   THEIR   DERIVATIVES     147 

of  chlorine  by  oxygen.  The  formula  of  the  resulting  compound 
would  be — 

H   OH 
I      I 
H— C— C  =  0    i.*.  CH3CO.OH 

H 

Monohydroxyl  derivatives  of  the  paraffin  hydrocarbons  are 

H 

called  alcohols.  Compounds  containing  the  group  — C=O 
are  known  as  aldehydes,  and  those  containing  — CO.OH  all 
possess  acidic  properties,  and  are  known  as  organic  acids. 

Chlor-substitution  compounds  corresponding  to  those  given 
above  can  be  derived  from  all  the  paraffins,  and  there  are  three 
homologous  series  of  oxygen  compounds  corresponding  to 
them — 

(a)  Alcohols  of  the  general  formula  CHH2rt  +  1OH 

(b)  Aldehydes   „          „  „       QH^O 

(c)  Acids  n          „  „       CMH2/t  _  jO  .  OH 

Alcohols.— CnH2n  +  iOH.  Methyl  hydroxide,  CH3OH,  or 
methyl  alcohol,  the  first  member  of  this  series,  is  the  hydroxyl 
derivative  of  methane.  It  is  produced  in  considerable  quantity 
by  the  destructive  distillation  of  wood  and  in  the  crude 
(unpurified)  state  is  commonly  called  "wood  spirit"  (p.  118). 
Pure  methyl  alcohol  is  a  colourless,  volatile,  neutral  liquid. 
It  has  a  faint  characteristic  odour  and  taste.  It  readily  burns 
in  the  air,  forming  carbon  dioxide  and  water  l— 

CH3OH  +  3O  ->  C02  +  2H2O 

Ethyl  alcohol  (C2H5OH)  is  the  common  alcohol,  or  "  spirit 
of  wine."  It  was  to  this  substance  that  the  name  alcohol2 
was  originally  given,  and  the  name  was  only  extended  to  other 
members  of  the  series  because  it  was  found  that  they  all 
possess  very  similar  properties  and  are  all  hydroxyl  derivatives 

1  The  complete  combustion    of  compounds    containing   carbon  and 
hydrogen  always  gives  carbon  dioxide  and  water. 

2  The  name  is  of  Arabic  origin. 


148     A   FOUNDATION   COURSE   IN   CHEMISTRY 

of  hydrocarbons.  It  then  became  necessary,  in  order  to  dis- 
tinguish the  different  kinds  of  alcohol,  to  add  another  word 
(methyl,  ethyl,  etc.),  corresponding  to  the  name  of  the 
hydrocarbon  from  which  the  particular  alcohol  is  derived.1 

Common  (ethyl)  alcohol  is  generally  obtained  by  the 
fermentation  of  sugars,  which  occur  naturally  in  the  juice 
of  fruits  or  are  produced  by  a  preliminary  treatment,  from 
starchy  grains.  The  fermentation  of  sugars  is  caused  by 
certain  organisms  like  yeast,  which  are  always  found  adhering 
to  the  outside  of  the  fruit.  When  the  fruit  is  crushed,  the 
organisms  become  mixed  with  the  juices  and  so  cause  the 
change  by  which  the  juice  is  converted  into  wine.  In  order  to 
set  up  fermentation  in  the  sugary  liquor  extracted  from  malt,  it 
is  necessary  to  add  yeast,  but  the  change  takes  place  in  much 
the  same  way.2  The  alcohol  so  produced  may  be  separated 
from  water,  and  other  constituents  of  these  fermented  liquors 
by  distillation.  This  is  how  it  came  to  be  called  spirit  of 
wine.3 

The  resemblance  between  pure  ethyl  and  methyl  alcohols 
is  so  close  that  it  is  very  difficult  to  distinguish  one  from  the 
other  or  to  separate  them.  The  chief  difference  is  that  methyl 
alcohol  boils  at  about  67°  C.  and  ethyl  alcohol  at  78°  C.  This 
of  course  is  merely  a  particular  case  of  the  general  rule  that, 
in  any  homologous  series,  the  members  which  contain  a  larger 
number  of  carbon  atoms  boil  at  a  higher  temperature. 

Ethyl  alcohol  also  burns  with  a  non-luminous  (and  there- 
fore non-smoky)  flame.  It  is  used  as  a  fuel  in  the  so-called 
"spirit-lamps."  It  is  also  used  as  a  solvent  for  gums  and 
resins  in  the  manufacture  of  varnish,  and  in  many  other  industrial 
processes. 

1  The  term  "alcohol  "  is  therefore  the  name  not  of  one  substance  but 
of  a  large  class  of  substances. 

2  Further  discussion  as  to  the  nature  of  fermentation  will  be  found  on 
p.  174. 

3  Although  ethyl  alcohol  boils  at  78°  C.  and  water  at  100°  C.,  it  is  not 
possible  to  separate  these  liquids  by  distillation  only,  though  a  product  con- 
taining about  96  per  cent,  of  alcohol  can  be  obtained  in  this  way.  To 
complete  the  drying,  the  distillate  must  be  allowed  to  remain  in  contact 
with  quick-lime  for  some  time  and  then  redistilled.  The  quick-lime  com- 
bines with  the  water.  The  ordinary  drying  agents,  calcium  chloride  and 
sulphuric  acid,  cannot  be  used,  for  both  combine  with  the  alcohol. 


PARAFFINS   AND   THEIR   DERIVATIVES      149 

As  a  constituent  of  wine  and  other  alcoholic  beverages, 
it  is  subject  to  a  very  high  duty.  This  tax  is  remitted  when 
the  alcohol  is  used  for  burning  and  for  industrial  purposes, 
provided  that  ten  per  cent,  of  crude  wood  spirit  is  added  to 
it,  so  as  to  render  it  unfit  for  drinking  purposes.  This  mixed 
product  is  called  methylated  spirit.  A  more  recent  enactment 
requires  the  addition  of  one  per  cent,  of  mineral  naphtha  to 
methylated  spirit,  but  this  requirement  may  be  dispensed  with 
in  certain  cases.  The  presence  of  the  naphtha  is  shown  on 
the  addition  of  water,  when  a  cloudiness  is  produced,  owing  to 
the  fact  that  the  water  does  not  dissolve  the  mineral  oil. 

Propyl  and  butyl  alcohols  are  respectively  derived  from 
propane  and  butane.  They  also  resemble  ethyl  alcohol,  but 
boil  at  higher  temperatures  according  to  the  number  of  carbon 
atoms  they  contain. 

Aldehydes. — CMH2nO.  The  aldehydes,  as  has  been  pointed 
out,  may  be  regarded  as  the  oxygen  derivatives  of  hydro- 
carbons, corresponding  to  the  dichlor-substitution  products. 
They  are  generally  prepared  by  the  gentle  oxidation  of 
alcohols,  but  may  also  be  obtained  by  the  reduction  of  acids 

(P-  IS2)- 

To   prepare  ethyl  aldehyde,  C2H4O,  i.e.  CH3CHO,  ethyl 

alcohol  and  sulphuric  acid  are  added  to  a  solution  of  potassium 
bichromate  in  a  flask.  The  potassium  bichromate  acts  as  the 
oxidising  agent,  and  the  action  generally  commences  without 
the  application  of  heat.  In  any  case  very  gentle  warming 
is  sufficient.  The  aldehyde  which  is  formed  is  a  volatile 
liquid,  boiling  at  21°  C.,  it  has  a  characteristic  fruity  odour. 

CH3CH2OH  +  O  ->  CH3CO.H  +  H2O 

Methyl  aldehyde  CH2O,  i.e.  H.COH,  cannot  be  prepared 
from  methyl  alcohol  in  the  same  manner,  but  is  formed  when 
a  mixture  of  the  vapour  of  the  alcohol  and  air  is  passed  over 
a  heated  spiral  of  platinum  wire.  Both  of  these  aldehydes  are 
soluble  in  water  and  in  alcohol  in  all  proportions. 

The  aldehydes  are  powerful  reducing  agents.  If  an  aqueous 
solution  of  an  aldehyde  and  a  few  drops  of  ammonia  be 
added  to  silver  nitrate  solution,  on  warming,  metallic  silver  is 


150     A   FOUNDATION    COURSE   IN   CHEMISTRY 

deposited.1  If  also  to  a  solution  of  copper  (cupric)  sulphate, 
a  drop  or  two  of  a  solution  of  an  aldehyde  be  added  and 
then  caustic  soda,  a  red  precipitate  of  cuprous  oxide  is  thrown 
down  on  warming. 

In  these  reducing  actions,  the  aldehyde  is  oxidised  forming 
an  acid — 

CH3CHO  +  O  ->  CH3 .  CO  .  OH  acetic  acid. 
H .  CHO  +  O  -»  H .  COOH  formic  acid. 

For  this  reason  ethyl  aldehyde  and  methyl  aldehyde  are 
generally  referred  to  as  acetic  aldehyde  and  formic  aldehyde, 
names  which  are  sometimes  further  contracted  into  acetaldehyde 
and  formaldehyde. 

Formaldehyde  has  never  been  obtained  in  a  pure  condition, 
but  a  solution  in  water  known  as  formalin  is  largely  used  as  an 
antiseptic.  It  is  used  as  a  preservative  for  milk  and  other 
foods. 

One  of  the  chief  properties  of  aldehydes  is  their  power  of 
combining  with  other  substances.  Thus,  with  hydrogen  they 
form  alcohols,  with  oxygen,  acids.  They  also  combine 
directly  with  ammonia,  hydrocyanic  acid,  and  with  alkaline 
sulphites. 

If  acetic  aldehyde  be  allowed  to  stand,  it  combines  with 
itself,  i.e.  it  undergoes  condensation,  forming  more  complex 
molecules,  though  the  proportion  between  the  elements 
remains  the  same.  Thus,  if  a  few  drops  of  sulphuric  acid 
be  added  to  acetic  aldehyde,  the  solution  becomes  hot,  and 
on  cooling  to  o°  C.  crystallises.  The  substance  formed  is 
called  paraldehyde,  and  its  formula  is  C6Hi2O3,  i.e.  3  mole- 
cules of  aldehyde  united.  Under  other  conditions  another 
solid  product  is  formed,  known  as  metaldehyde.  The  formula 
of  this  is  unknown,  as  it  is  not  easily  soluble  in  any  solvent, 
and  on  vaporising,  it  is  reconverted  into  aldehyde.2  These 

1  Glass  mirrors  are  sometimes  made  in  this  way. 

2  When  a  solution  of  acetaldehyde  is  warmed  with  strong  caustic  potash, 
the  liquid  becomes  yellow,  and  an  amorphous  yellowish  red  precipitate 
separates  after  a  short  time.     This  is  known  as  aldehyde  resin.     If,  how- 
ever, a  very  dilute  caustic  potash  solution  be  employed  (or  sodium  acetate,  or 
zinc  chloride)  instead  of  strong  caustic  alkali,  the  aldehyde  undergoes  con- 
densation and  a  substance  is  formed  having  the  formula  C4H8O2.     Now, 


PARAFFINS   AND   THEIR   DERIVATIVES      151 

two  compounds  are  said  to  be  polymeric  modifications  of 
aldehyde. 

The  name  "  aldehyde  "  was  given  to  these  compounds 
because  of  their  preparation  from  alcohol.  The  action  of 
the  oxidiser,  potassium  bichromate,  may  be  indicated  by  the 
equation  — 

C2H5OH  +  O->CH3COH  +  H2O 

from  which  it  will  be  seen  that  the  action  of  the  oxygen 
may  be  considered  as  taking  two  atoms  of  hydrogen  from 
the  alcohol  molecule.  The  resulting  compound  was  therefore 
first  known  by  the  "  Latin  "  term  («/)cohol  (^?/$)v/)rogenatum, 
i.e.  alcohol  dehydrogenated,  a  term  which  has  been  contracted 
as  indicated  by  the  brackets.  By  continuing  the  action  of 
potassium  bichromate,  the  aldehyde  may  be  further  oxidised  to 
the  corresponding  acid. 

Formic  aldehyde  may  be  looked  upon  as  a  simple  member 
of  a  class  of  compounds  known  as  carbohydrates  (p.  170). 
These  compounds  contain  carbon,  hydrogen,  and  oxygen,  the 
hydrogen  and  oxygen  being  present  in  the  same  proportions  as 
in  water.  If  the  formula  for  formaldehyde  be  written  CH2O, 
the  resemblance  is  obvious.  Moreover,  it  has  been  shown 
that  probably  formaldehyde  is  formed  in  plants  from  the 
carbon  dioxide  and  water  vapour  which  they  inhale  through 
the  stomata  of  their  leaves.  It  is  well  known  that  the  action 
of  the  plants  in  the  presence  of  sunlight  is  to  assimilate  the 
carbon  of  the  carbon  dioxide  and  to  liberate  its  oxygen. 
This  is  probably  done  according  to  the  following  equation  — 


(Formaldehyde.) 

It  is  quite  possible  that  the  formaldehyde  thus  formed  may 
undergo  a  kind  of   condensation   and   form   more   complex 

acetaldehyde  is  C2H4O,  and  therefore  the  substance  formed  is  quantitatively 
equal  to  2(C2H4O).  It  is  known  as  aldol,  and  its  formation  may  be  repre- 
sented as  follows  :  — 

H  H  H  H 

CH3.C          +H.CHo.C         ->CH3.C  --  CH2  .  C 

\    /^  \  \  \ 

O^  O  OH  O 


152     A    FOUNDATION    COURSE    IN   CHEMISTRY 

molecules  (cp.  paraldehyde).  From  the  chemical  point  of 
view,  the  possibility  is  well  established,  for  formaldehyde,  by 
the  action  of  lime  water,  undergoes  condensation  of  this  kind 
and  forms  a  sweet,  syrupy  substance  which  is  a  mixture  of 
compounds  having  the  formula  CeH^Oe1  (equal  quantitatively 
to  6CH2O).  It  is  known  as  formose.  If  an  action  similar  to 
this  takes  place  in  plants,  and  a  compound  C6H12O6  be  formed, 
starch  might  possibly  be  formed  afterwards  by  the  abstraction 
of  water. 


Acids.  -CnH2n_!O  .  OH  or  C^^+jCOOH  or 

When  alcohols  or  aldehydes  are  strongly  oxidised,  the  two 
hydrogen  atoms  attached  to  the  carbon  which  is  already  partly 
oxidised  are  replaced  by  oxygen,  according  to  the  equation  — 

CH3  .  CH2OH  +  Oa  ->  CH3.CO.OH  +  H2O 

The  compounds  so  produced  turn  blue  litmus  red,  combine 
with  bases  to  form  salts  with  the  liberation  of  water,  and  in 
general  exhibit  all  the  characteristic  properties  of  acids. 

The  acids  corresponding  to  the  first  few  members  of  the 
series  of  paraffin  hydrocarbons  are  — 

(1)  Formic  acid,  HCOOH,  from  CH4. 

(2)  Acetic  acid,  CHSCOOH,  from  C2H6. 

(3)  Propionic  acid,  QH^OOH,  from  C3H8. 

(4)  Butyric  acid,  C3H7COOH,  from  C4H]0. 

As  before  stated  they  may  be  considered  as  corresponding 
to  the  trichlor-substitution  products  of  the  hydrocarbons— 

/$ 
Thus        CH4  -»  CHC1,  ->  CH  le.  H  .  COOH 


x 


Q  £[  (  Formic  acid.  ) 


The  first  member  of  the  series,  formic  acid,  derives  its 
name  from  the  fact  that  it  is  found  in  the  bodies  of  red  ants.2 
It  also  occurs  in  stinging  nettles  (  Urtica  dioicd]  ;  the  pain  of  the 
sting  is  probably  caused  by  the  injection  of  a  small  amount 


1  Aldol  condensation  (p.  151,  note). 

2  Latin,  formica,  an  ant. 


PARAFFINS   AND   THEIR   DERIVATIVES      153 

of  formic  acid  secreted  by  the  leaf  of  the  plant.  It  can  be 
formed  from  methyl  alcohol  by  oxidation  ;  also  synthetically 
by  submitting  a  mixture  of  carbon  monoxide  and  steam,  or 
carbon  dioxide  and  hydrogen,  to  the  action  of  the  silent  electric 
discharge.  The  salts  of  formic  acid  are  known  as  formates. 
Potassium  formate  can  be  made  by  neutralising  the  acid  with 
caustic  potash  or,  in  a  more  interesting  manner,  by  the  action 
of  carbon  monoxide  upon  strong  caustic  potash  at  100°  C.  — 

CO  +  KOH->H.COOK 

or  again,  by  allowing  moist  carbon  dioxide  to  act  upon  metallic 
potassium  — 

3CO2  +  4K  +  H,O  ->  2H.COOK  +  K2CO3 

It  is  also  formed  from  hydrocyanic  acid  (p.  179),  but  is 
generally  prepared  by  distilling  oxalic  acid  with  glycerine. 

Formic  acid  and  formates  evolve  carbon  monoxide  when 
treated  with  sulphuric  acid  (p.  124)  — 


HjCOiOH  +  H2SO4->  H2SO4  +  H2O  +  CO 

HJCOJONa  +  H2S04  ->  NaHSO4  4-  H2O  +  CO 
' 


Acetic  acid,  CH3COOH,  the  second  member  of  the  series, 
is  derived  by  oxidation  from  ethyl  alcohol.  It  is  one  of  the 
products  obtained  in  the  destructive  distillation  of  wood 
(p.  1  1  8).  When  weak  wine  is  exposed  to  the  air,  it  turns 
sour  owing  to  the  formation  of  acetic  acid  by  oxidation  of  the 
alcohol.  The  change  is  promoted  by  the  action  of  certain 
micro  organisms,  and  is  in  fact  a  kind  of  fermentation.2  The 
product  was  called  vinegar,  but  in  this  country  the  liquid 
commonly  sold  under  that  name  is  now  manufactured  by 
acetic  fermentation  of  other  alcoholic  liquors. 

1  Compare  this  decomposition  with  the  synthesis  of  formic  acid  from 
carbon  monoxide  and  water  and  of  formates  from  carbon  monoxide  and 
caustic  alkali. 

2  The  organism  chiefly  employed  in  acetic  acid  fermentation  is   that 
known  as  "  mycoderma  aceti"  (Gk.  HVKTJS,  a  mushroom  or  fungus;  5ep,ua, 
skin),  or  bacterium  aceti. 


154     A   FOUNDATION   COURSE    IN    CHEMISTRY 

The  production  of  vinegar l  is  carried  on  by  allowing  dilute 
alcohol  (wine,  beer,  etc.)  to  drop  upon  shavings  which  have 
been  first  steeped  in  vinegar  to  provide  the  micro  organism. 
The  shavings  have  the  effect  of  distributing  the  alcohol  over 
a  large  surface  and  so  quickening  the  oxidation  of  the 
alcohol.  Commercial  acetic  acid  is  generally  made  by  the 
distillation  of  wood. 

When  pure,  the  acid  is  a  colourless  liquid,  which  becomes 
solid  at  a  temperature  of  i6'6°  C.  In  this  state  it  much 
resembles  ice  in  appearance,  and  is  therefore  called  glacial 
acetic  acid. 

The  salts  of  acetic  acid  are  known  as  acetates,  that  of 
sodium  is  CH3COONa.  When  the  acetates  of  the  alkalies 
are  heated  strongly  with  caustic  soda  or  lime,  they  yield  marsh 
gas  (p.  139)— 

CH3COONa  +  NaOH  ->  Na2CO3  +  CH4 

All  the  acids  of  this  series  are  monobasic  (p.  57).  No 
matter  how  many  hydrogen  atoms  they  contain,  only  the 
hydrogen  of  the  hydroxyl  group  can  be  replaced  by  a  metal. 
(In  the  acids  whose  formulae  are  given  on  page  152,  the 
hydrogen  which  is  replaceable  is  underlined.) 

The  formula  for  the  acetate  of  a  monad  element  such 
as  sodium  is  therefore  CH3CO.ONa,  for  a  diad  element — 

|Ca        U        (CH3CO.O)2Ca 

the    corresponding   butyrates   would    be    C3H7COONa  and 
(C3H7CO.O)2Ca. 

Esters. — The  formula  for  ethyl  alcohol  is  always  written 
CH3CH2OH  or  C2H5OH  (not  C2H6O),  because  the  substance 
exhibits  many  of  the  characteristic  properties  of  a  hydroxide. 
As  a  matter  of  fact  it  is  often  called  ethyl  hydroxide.  Like 
ammonium  hydroxide  (NH4OH)  it,  and  the  other  alcohols, 
can  form  compounds  with  acids,  which  can  be  looked  upon 
as  salts.  Thus  we  have  ethyl  acetate,  ethyl  sulphate,  ethyl 
butyrate,  and  so  on.  Such  compounds  of  the  alcohols  with 
acids  are  called  ethereal  salts  or,  more  shortly,  esters.  The 

1  Acetic  acid  derives  its  name  from  the  Latin,  acetum  =  vinegar. 


PARAFFINS   AND   THEIR   DERIVATIVES      155 

method  of  preparation  of  these  esters  can  be  illustrated  by  that 
of  ethyl  acetate. 

The  equation  representing  the  reaction  may  be  written — 


CH3COOH  +  C2H5OH^CH3COOC2H5  +  H2O 


The  ester  is  not  satisfactorily  prepared  by  merely  mixing 
the  alcohol  and  the  acid,  for,  as  the  equation  represents, 
the  action  is  reversible,  and  not  only  does  acetic  acid  act 
upon  alcohol  giving  ethyl  acetate  and  water,  but  water  reacts 
with  ethyl  acetate,  giving  again  the  acid  and  the  alcohol. 
A  condition  of  equilibrium  is  therefore  reached  in  which  the 
two  reactions  just  balance  one  another,  unless  something  is 
put  into  the  mixture  to  remove  the  water  which  is  produced. 
The  material  generally  employed  is  concentrated  sulphuric  acid, 
and  if  a  mixture  of  acetic  acid  (or  sodium  acetate),  alcohol, 
and  concentrated  sulphuric  acid  be  distilled,  ethyl  acetate  can 
be  collected,  as,  owing  to  the  presence  of  the  sulphuric  acid 
and  the  consequent  removal  of  the  water,  the  reaction  only 
proceeds  in  one  direction,  and  will  go  on  to  completion — 

CH3COOH  +  f  2H5OH  +  H2SO4 

->  H2S04  +  H2O   +  CH3COOC2H5 

The  method  given  may  be  taken  as  typical  of  that  employed 
in  the  general  production  of  esters. 

The  alcohols  have  not  the  strongly  basic  properties  of 
ammonium  hydroxide,  or  of  most  of  the  metallic  hydroxides,  and 
the  ethereal  salts  are  not  stable  like  the  salts  of  ammonium  and 
of  metals,  as  is  shown  by  their  easy  decomposition  with  water. 

Many  esters  similar  to  ethyl  acetate  occur  in  nature,  and 
many  are  made  and  sold  as  "fruit  essences."  Thus  ethyl 
butyrate,  C3H7COOC2H5,  is  known  as  essence  of  pineapple, 
while  amyl1  acetate,  CHjjCOOCgHn,  is  sold  as  essence  of 
Jargonelle  pear. 

1  Amyl  alcohols  are  those  of  the  formula  C5HUOH.  One  of  them 
forms  the  chief  ingredient  in  "fusel  oil."  ^  This  is  formed  during  the 
fermentation  of  sugar  solutions  with  yeast  (wine,  beer,  etc.),  and  is  present 
in  freshly  distilled  spirits. 


156     A   FOUNDATION   COURSE    IN   CHEMISTRY 

Waxes  are  compounds  of  a  similar  nature.  They  are 
formed,  however,  from  the  alcohols  containing  many  carbon 
atoms  (higher  alcohols),  and  acids  of  a  similarly  complex 
nature.  Thus  spermaceti  is  cetyl  palmitate,  C15H31COOC1GH33. 
Bees'  wax  is  a  mixture  of  cerotic  acid,  C^H^COOH,  with 
myricyl  palmitate,  C15H31COOC3oH61. 

The  so-called  paraffin  wax  (p.  140)  does  not  belong  to 
this  class.  Some  of  the  higher  fats,  such  as  Japan  wax,  are 
commercially  known  as  waxes  because  they  resemble  them 
in  appearance. 

Fats  are  closely  related  to  the  ethereal  salts,  but  they  are 
of  such  importance  that  they  will  receive  special  treatment 
later. 

defines. — When  alcohol  is  mixed  with  concentrated 
sulphuric  acid,  heat  is  developed,  owing  to  the  combination 
of  the  alcohol  with  the  acid,  and  the  consequent  formation 
of  water.  The  compound  produced  by  this  reaction,  however, 
is  not  ethyl  sulphate,  (C2H5)2SO4,  but  ethyl  hydrogen  sulphate, 
C2H5HSO4,  a  compound  corresponding  to  ammonium  hydrogen 
sulphate  or  sodium  hydrogen  sulphate — 

C2H5OH  +  H2S04->  C2H5HS04  +  H2O 

When  this  compound  is  heated  it  is  decomposed  as  shown 
in  the  following  equation — 

C2H5HSO4->  C2H4  +  H2SO4 

The  hydrocarbon  C2H4  is  called  ethylene.  In  preparing 
it,  there  is  no  need  to  separate  the  ethyl  hydrogen  sulphate. 
It  is  sufficient  to  mix  alcohol  with  concentrated  sulphuric  acid 
and  heat  the  mixture.  The  gas  is  given  off  accompanied  by 
small  quantities  of  ether,  and,  as  a  certain  amount  of  carboni- 
sation always  takes  place,  sulphur  dioxide  and  carbon  dioxide 
are  also  formed.  These  are  removed  by  passing  the  gas 
through  dilute  alkali. 

Ethylene  is  a  hydrocarbon  of  a  type  different  from  the 
paraffins,  for  unlike  these  it  can  form  compounds  without 
parting  with  any  hydrogen.  For  example,  it  combines  directly 
with  chlorine,  forming  no  hydrochloric  acid,  but  yielding  an 
oily  liquid  of  the  formula  C2H4C12.  In  other  words,  chlorine 


PARAFFINS   AND   THEIR   DERIVATIVES      157 

can  be  directly  added  to  it.  As  this  is  possible  it  is  obvious 
that  the  carbon  in  'the  compound  is  not  combined  with  all  that 
it  could  combine  with.  Ethylene  is  therefore  an  unsaturated 
hydrocarbon,  its  condition  of  unsaturation  being  shown  by  the 
fact  that  it  takes  up  chlorine,  without  formation  of  hydrochloric 
acid,  and  forms  an  addition  compound.  Saturated  hydro- 
carbons can  only  form  substitution  compounds. 

The  chlorine  derivative  is  known  as  ethylene  dichloride; 
we  have  previously  met  with  a  compound  of  the  same  empirical 
formula,  but  the  two  are  very  different  in  their  properties. 
Dichlorethane  Q>H4C12  is  represented  by  the  formula  CH3CHC12 
(p.  145),  but  all  experiments  tend  to  prove  that  in  ethylene 
dichloride  the  two  chlorine  atoms  are  combined  with  different 
carbon  atoms,  and  its  formula  must  therefore  be  written 
CH2Cl.CHaCl. 

This  can  be  expressed  graphically — 

H\ 

>C— Cl 

H/ 

H\ 

>C— Cl 

H/ 

As  ethylene  is  simply  this  compound  without  the  chlorine, 
it  might  be  written — 

CH2 

CHo 

but  this  would  suggest  that  carbon  was  trivalent,  and  would 
not  show  why  it  should  take  up  chlorine  so  easily.  We  there- 
fore write  the  formula — 

CH,,1 

II 
CH2 

1  The  lines  drawn  in  these  formulae  about  the  carbon  atom  and  others 
must  not  be  materialised  in  any  way.  The  double  bond  in  this  formula 
does  not  signify  that  the  two  carbon  atoms  are  tied  together  by  two  strings 
instead  of  one,  or  anything  like  that.  It  means  rather,  that  in  the  com- 
pounds in  which  it  appears,  the  carbon  has  a  reserve  valency  which  can  be 
utilised  when  occasion  arises.  It  is  the  sign  of  nn  saturation. 


158     A   FOUNDATION   COURSE   IN   CHEMISTRY 

By  replacing  a  hydrogen  atom  in  ethylene  by  methyl 
(CH3)  we  obtain  another  hydrocarbon,  C3H6.  This  is  known 
as  propylene.  Also  by  replacement  of  a  hydrogen  atom  in 
propylene  by  CH3  we  obtain  C4H8,  butylene,  and  so  on.  In 
short,  we  have  another  homologous  series  of  hydrocarbons 
which  may  be  represented  by  the  general  formula  CnH2/l. 

The  formation  of  the  oily  compound  C2H4C12  when  chlorine 
is  added  to  ethylene,  caused  that  gas  to  receive  the  name  of 
olefiant1  gas.  The  name  with  a  modification  is  extended  to  the 
whole  series.  The  hydrocarbons  belonging  to  it  are  known  as 
the  Olefines. 

Ethylene  is  colourless,  and  insoluble  in  water.  It  burns  with 
a  brightly  luminous  flame,  and  its  density  compared  with 
hydrogen  is  14,  i.e.  its  molecular  weight  is  28.  (Note  that  it  is 
only  very  slightly  lighter  than  air.) 

A  still  more  unsaturated  hydrocarbon  is  obtained  by  the 
direct  union  of  carbon  and  hydrogen  at  the  temperature  of  the 
electric  spark.  This  compound  is  acetylene.  It  is  a  colourless 
gas  with  a  disagreeable  odour,  poisonous,  and  burns  with 
a  brightly  luminous  flame.  If  burned  without  sufficient  air 
supply  it  yields  large  quantities  of  soot.2  Its  density  compared 
with  hydrogen  is  13,  and  its  molecular  weight  therefore  26. 
This  and  its  analysis  show  that  its  formula  must  be  written 
C2H2.  The  gas  can  take  up  four  atoms  of  chlorine  forming  a 
tetrachloride,  C2H2C14.  Its  condition  of  unsaturation  is 
represented  by  its  formula — 

C— H 

II! 
C— H 

Acetylene  is  often  formed  when  a  bunsen  burner  "  strikes 
back ; "  the  odour  can  then  be  recognised. 

As,  however,  the  gas  is  largely  used  for  illuminating 
purposes,  a  more  convenient  method  of  preparing  a  large 
quantity  is  used.  This  is  the  action  of  water  upon  calcium 
carbide,  CaC2 — 

CaC2  +  2H20  ->  C2H2  -f  Ca(OH)2 

1  Lat.  oleum,  oil ;  fio,  I  become. 
3  See  note  A  at  the  end  of  this  chapter  (p.  185). 


PARAFFINS   AND   THEIR   DERIVATIVES      159 
As  acetylene  is  represented  by  the  formula — 

C.H 

III 
C.H 

/C 
calcium  carbide  must  be  Ca<   ||| 

\C 

Flame. — The  increasing  luminosity  of  the  flames  of 
hydrogen,  marsh  gas,  ethylene,  and  acetylene  as  the  amount  of 
carbon  in  the  molecule  is  increased  is  significant.  The  flame 
of  burning  hydrogen  is  almost  non-luminous,  while  that  of 
acetylene  burning  under  favourable  conditions  is  of  dazzling 
brightness. 

The  luminosity  of  flame  is  generally  due  to  the  presence 
of  incandescent  solid  particles.  A  bunsen  flame  is  almost  non- 
luminous,  but  if  a  piece  of  platinum  wire  be  suspended  in  it, 
the  wire  becomes  white  hot  and  emits  light.  The  introduction 
of  a  solid  into  the  flame  for  the  purpose  of  producing 
luminosity  is  also  seen  in  the  case  of  the  incandescent  gas 
mantle.  The  flame  in  which  the  mantle  hangs  would  be 
almost  non-luminous,  but  the  solid  mantle  glows  brightly.1 

If  a  piece  of  cold  porcelain  or  glass  be  placed  for  a  moment 
in  an  ordinary  luminous  gas  flame,  it  becomes  covered  with 
a  coating  of  soot,  i.e.  particles  of  carbon.  This,  however, 
scarcely  shows  the  presence  of  solid  particles  in  the  flame,  as 
the  introduction  of  the  cold  substance  may  merely  alter  the 
condition  existing  in  that  part  of  the  flame — it  may  cool  the 
flame  so  that  combustion  partially  ceases.  The  presence  of 
solid  particles  in  the  luminous  portion  of  a  gas  flame  can, 
however,  be  inferred  from  the  following  experiment,  which  is 
best  performed  on  a  bright  sunshiny  day.  As  is  well  known, 
it  is  possible  by  means  of  a  lens  to  form  an  image,  say,  of  the 
sun  upon  a  solid  surface,  but  such  an  image  cannot  be  formed 

1  These  mantles  are  composed  of  a  mixture  of  thorium  oxide  (ThO2) 
and  cerium  oxide  (CeO2),  99  per  cent,  of  the  former  and  I  per  cent,  of 
the  latter. 

The  use  of  a  solid  to  produce  luminosity  is  also  well  seen  in  the  lime- 
light, in  which  the  hot  flame  of  hydrogen  or  coal  gas  burning  in  oxygen  is 
projected  on  to  a  cylinder  of  quick -lime. 


160     A   FOUNDATION    COURSE   IN   CHEMISTRY 


upon  a  liquid  or  a  gas.  If  now  an  ordinary  bat's-wing  burner 
be  lighted,  and  a  lens  held  near  it  in  the  sunshine,  it  will  be 
found  possible  to  focus  an  image  of  the  sun  as  a  highly 
luminous  spot  upon  the  brightest  portion  of  the  flame.  This 
would  not  be  possible  unless  the  flame  were  solid,  or  contained 
huge  numbers  of  solid  particles  acting  as  a  solid  screen.  The 
experiment  therefore  proves  that  the  luminous  portion  of  such 
a  flame  contains  solid  particles,  and  as  the  ordinary  burner 
burns  coal  gas,  the  only  possible  solid  particles  are  those  of 
carbon.1 

It  must  not  be  assumed,  however,  that  a  flame  cannot  be 
luminous  without  solid  particles.  The  flame  of  hydrogen 
becomes  somewhat  luminous  when  the  gas  and  the  oxygen  in 
which  it  is  burning  are  under  pressure.  Also,  when  carbon 
bisulphide  burns  in  nitric  oxide  the  flame  is  intensely  luminous, 
and  in  this  case  no  solids  are  present,  and  no  extra  pressure  is 
applied  to  the  gas. 

In  the  case  of  the  flames  of  methane,  ethylene,  and 
acetylene,  the  luminosity  is  due  to  the  presence  of  unburnt 
particles  of  carbon,  and  as  there  is  a  larger 
percentage  of  carbon  in  acetylene  than  in  the 
others,  the  flame  of  this  gas  is  the  most  luminous 
of  the  three. 

Structure  of  the  Flame. — The  flame  of  an 
ordinary  candle  may  be  taken  as  typical.  It 
consists  of  three  parts,  which  we  will  refer  to 
as  A,  B,  C. 

A  is  in  appearance  dark  blue  in  tint.     It 
consists  of  the  volatilised  hydrocarbons  of  which 
the  candle  is  composed.     It  is  not  in  contact 
with  the   oxygen  of  the   air,  and  is  therefore 
not  within  the  area  of  combustion.     B  is  the 
luminous  portion.     It  surrounds  A  on  all  sides, 
and  occupies  the  greater  portion  of  the  flame.     It  is  the  area 
of  partial  combustion,  and  it  is  here  that  the  solid  particles 
formed  by  decomposition  of  the  material  of  the  candle  are  to 


FIG.  18. 


1  The  brilliancy  of  the  flame  of  burning  magnesium  is  due  to  incan- 
descence of  the  oxide  formed. 


PARAFFINS   AND   THEIR   DERIVATIVES      161 

be  found.  As  they  pass  outwards  they  gradually  reach  the 
part  of  the  flame  where  it  is  in  direct  contact  with  the  oxygen 
of  the  air,  and  combustion  becomes  complete.  This  is  the 
area  C,  which  consists  entirely  of  the  incandescent  products 
of  combustion  ;  in  this  case  carbon  dioxide  and  water  vapour. 
These  being  gases  are  only  faintly  luminous  and  can  barely 
be  seen. 

The  Bunsen  Flame. — Air  is  introduced  into  the  middle 
of  this  flame,  thereby  causing  complete  combustion,  not  only 
at  the  outside  but  inside  also.  The  solid  particles  are  there- 
fore absent,  and  the  flame  is  much  hotter. 

Ethers. — When  ethyl  hydrogen  sulphate  is  heated  by  itself 
it  splits  up  into  ethylene  and  sulphuric  acid,  but  when  heated 
with  excess  of  alcohol  a  different  change  occurs ;  the  products 
are  sulphuric  acid  and  ether — 

C2H5HSO4  +  C2H5OH  ->  (C2H5)2O  -}-  H2SO4 

Here  again  it  is  not  necessary  to  prepare  the  ethyl  hydrogen 
sulphate  as  a  separate  compound.  It  is  sufficient  to  mix 
together  sulphuric  acid  and  alcohol,  and  heat  the  mixture. 
The  temperature,  however,  must  not  exceed  140°  C.,  and 
alcohol  should  be  continually  added  at  such  a  rate  as  to  keep 
the  temperature  constant  at  this  point.  If  this  is  done,  the 
evolution  of  ether  is  continuous,  and  it  can  be  collected  in  a 
receiver  as  long  as  alcohol  is  supplied  to  the  mixture. 

The  nature  of  this  ether  is  most  easily  understood  by  com- 
paring its  constitutional  formula  with  that  of  water  and  alcohol. 
Water     .....     H— O— H 
Alcohol       ....     C2H5— O— H 
Ether     ."....     C2H5— 02— C2H5 

It  will  be  seen  that  in  the  ether  the  hydroxyl  hydrogen  atom 
is  replaced  by  another  ethyl  group.     The  ether  bears  much 
the   same  constitutional  relation  to  the  alcohol  as  potassium 
oxide  bears  to  potassium  hydroxide. 
Again  compare  the  formulae — 

Water H— O— H 

Potassium  hydroxide    .     .     K — O — H 
Potassium  oxide       .     .     .     K — Q— K 

M 


162     A   FOUNDATION   COURSE   IN   CHEMISTRY 

Ordinary  ether  may  therefore  be  looked  upon  as  the  oxide 
of  ethyl,  and  other  ethers  as  the  oxides  of  other  organic  radicles. 
Ethers,  however,  have  no  basic  properties  which  are  in  any 
degree  comparable  with  those  of  basic  oxides. 

Many  other  ethers  are  known;  such  are  methyl  ether 
(CHS)2O,  propyl  ether  (CSH7)2O,  and  methyl  ethyl  ether 


The  ether  commonly  found  in  the  laboratory  is  ethyl  ether. 
As,  however,  it  is  prepared  from  methylated  spirit  it  is  not 
quite  pure,  but  contains  a  minute  quantity  of  methyl  ether. 
It  is  a  limpid,  neutral,  mobile  liquid.  It  is  highly  volatile, 
its  boiling  point  being  34-9°  C.  It  burns  with  a  luminous 
flame,  and  the  mixture  of  its  vapour  with  air  is  highly  explosive. 
It  is  somewhat  soluble  in  water,  and  water  is  slightly  soluble 
in  ether.  Its  chief  uses  in  the  laboratory  arise  from  the  facility 
with  which  it  dissolves  fats  and  oils,  and  many  other  organic 
compounds.  It  does  not  act  as  a  solvent  towards  inorganic 
compounds.1  It  is  therefore  used  for  the  extraction  of  fats, 
from  which  it  is  easily  separated  by  distillation. 

Ether,  as  generally  supplied,  contains  a  considerable 
quantity  of  water  and  some  alcohol;  but  both  of  these 
impurities  are  removed  by  prolonged  contact  with  calcium 
chloride.  The  last  traces  of  water  can  be  taken  away  only 
by  the  addition  of  metallic  sodium. 

Polyhydric  Alcohols.  —  It  has  been  shown  that  dichlorethane 
and  ethylene  chloride  are  both  represented  by  the  same 
empirical  formula,  C2H4C12.  The  difference  in  properties 
has  been  traced  to  a  difference  in  constitution.  In  the  former 
the  two  atoms  of  chlorine  are  attached  to  the  same  carbon 
atom,  in  the  latter  they  are  attached  to  the  different  ones. 
This  is  indicated  by  the  constitutional  formulae  — 

CHs-CHCls  .     .     .     Dichlorethane. 
CH2C1  -  CH2C1     .     .     Ethylene  chloride. 

When  monochlorethane,  C^Cl  (ethyl  chloride),  is  treated 
with  silver  hydroxide,  the  chlorine  is  replaced  by  hydroxyl  and 
ethyl  alcohol  (C<>H5OH)  is  formed.     It  might  be  expected 
1  See  note  B  at  the  end  of  this  chapter. 


PARAFFINS   AND   THEIR   DERIVATIVES      163 

therefore,  that  when  dichlorethane  is  treated  in  a  similar  way 
each  of  the  chlorine  atoms  would  be  replaced  by  hydroxyl. 
As  a  matter  of  fact  this  does  not  occur;  water  is  always 
formed,  and  the  product  obtained  is  aldehyde  — 

/H 
CH3CHC12  +  2AgOH  ->  2AgCl  +  H2O 


It  may  be  taken  as  -a  rule,  to  which  there  are  very  few 
exceptions,  that  more  than  one  hydroxyl  group  is  never 
attached  to  the  same  carbon  atom.1 

When  ethylene  dichloride  is  treated  with  silver  hydroxide 
(moist  silver  oxide)  each  of  the  atoms  of  chlorine  is  replaced 
by  hydroxyl.  The  product  is  called  glycol  — 

(CH2Cl>,  +  2AgOH  ->  2AgCl  4-  (CH.,OH>, 

i.e.  C,H4(OH)a 

As  ethylene  dichloride  may  be  represented  thus  — 

CH2C1 

I 
CH2C1 

glycol  may  likewise  be  expressed  thus  — 

H    H 

CH.,OH  H—  C—  C—  H 

or  |       | 

CH2OH  O     O 

I       I 
H    H 

Any  compound  which  contains  hydroxyl  attached  to  a 
carbon  atom  not  otherwise  oxidised  has  the  characteristic 
properties  of  and  is  classed  as  an  alcohol.  It  will  be  seen, 
therefore,  that  glycol  is  a  double  alcohol,  or  as  it  is  commonly 
called,  a  dihydric  alcohol.  Just  as  the  alcohols  previously 
described  were  compared  to  the  hydroxide  of  the  monovalent 

1  The  non-existence  of  stable  carbonic  acid  is  an  instance.    Its  formula 

HOV 

H2CO3  would  be          Nc  =  O, 
HCK 


164     A   FOUNDATION   COURSE    IN   CHEMISTRY 

metal  potassium  KOH,  so  glycol  and  other  dihydric  ajcohols 
may  be  compared  to  the  hydroxide  of  a  divalent  metal  such 
as  calcium,  Ca(OH)2. 

It  was  pointed  out  that  the  term  "  alcohol "  was  extended  to 
include  the  whole  class  of  the  monohydroxyl  derivatives 
similar  to  "  spirit  of  wine."  In  like  manner  the  term  "  glycol " 
is  extended  to  include  all  the  dihydric  alcohols ;  they  are 
known  as  glycols. 

Trihydric  alcohols  containing  three  hydroxyl  groups  are 
known.  As  no  two  hydroxyl  groups  can  be  attached  to  the 
same  carbon  atom,  the  simplest  trihydric  alcohol  must  contain 
three  carbon  atoms.  It  will  be  C3H5(OH)3. 

This  is  glycerine.     Its  structural  formula  may  be  written — 

H    H     H 

I       I       I 
H— C— C— C— H 

I       I       I 
000 

I    I    I 

H    H    H 
or  CH2OH.CHOH.CH2OH 

For  the  sake  of  uniformity  in  nomenclature,  and  to  retain 
names  ending  in  "ol"  for  hydroxyl  derivatives,  glycerine  is 
generally  referred  to  in  chemistry  as  glycerol.1 

Glycerine  or  glycerol  is  a  colourless  syrupy  liquid,  with  a 
very  sweet  taste.  It  dissolves  in  alcohol  and  in  water  in  any 
proportion,  and  takes  up  moisture  from  the  air.-  It  cannot  be 
distilled  at  ordinary  pressure  as  it  undergoes  decomposition. 

Glycerol  may  be  compared  to  the  hydroxide  of  a  triad 
metal,  such  as  aluminium,  A1(OH)3.  It  will  form  salts,  with 
acids  as  the  mono  and  dihydric  alcohols  do;  the  triacetate 
may  be  taken  as  an  example.  Its  formula  is— 

(CH3COO)3C3H5         i.e.        CH3COO\ 

CH3COO— C3H5 
CH3COO/ 

1  Gk.  y\vKvs,  sweet. 

2  As  glycerine  does  not  dry  or  resinise,  it  is  used  in  making  ink  for 
use  with  rubber  stamps,  also  for  certain  forms  of  copying  inks. 


PARAFFINS   AND   THEIR   DERIVATIVES      165 

Pats,  Oils,  and  Soap.  —  Most  people  know  that  soap  is  made 
by  boiling  fats  with  soda.  Many  of  the  older  generation  of 
country  folk  were  accustomed  to  make  their  own  soap  in  this 
way.  Glycerol  is  produced  at  the  same  time.  Ordinary  soap 
consists  largely  of  sodium  stearate,  i.e.  the  sodium  salt  of 
stearic  acid.  Stearic  acid  is  one  of  the  higher  members  of  the 
homologous  series  to  which  acetic  acid  belongs,  and  to  which 
the  general  formula  CMH2n  +  1COOH  has  been  assigned.  Its 
formula  is  C17H;,5COOH. 

From  the  change  which  takes  place  when  fat  is  boiled  with 
soda,  it  can  be  seen  that  the  fat  is  a  compound  of  stearic  acid 
and  glycerol.  It  is,  in  fact,  glycerol  tristearate  —  an  ester. 

The  reaction  with  caustic  soda  may  therefore  be  repre- 
sented thus  :  — 


C17Hi5COO-  QH5  +  3NaOH  =  3C17H35COONa  +  C3H5(OH)3 


Sodium  stearate  Glycerol. 

Fat.  (soap). 

It  is  well  known  that  the  soaps  prepared  from  different 
kinds  of  fats  have  not  exactly  the  same  properties.  Some  of 
them  are  salts  of  other  acids,  the  most  important  of  which  are 
palmitic  acid  C15H31COOH,  and  oleic  acid  C17H$3COOH,  but 
as  glycerol  is  always  liberated  during  the  process  of  manu- 
facturing them,  we  may  conclude,  therefore,  that  the  fats  from 
which  such  soaps  are  produced,  are  compounds  of  these  acids 
with  glycerol. 

These  salts  of  glycerol  are  often  called  glycerides,  and  are 
also  referred  to  by  names  ending  in  "  in."  Thus  — 

Glyceryl  tristerate      =  stearin     =  the  glyceride  of  stearic  acid. 
„       tripalmitate  =  palmitin  =     „         „  palmitic  „ 

„       trioleate       =  olein        =     „         „  oleic        „ 

Fats  occur  in  nature  as  products  of  animal  or  vegetable 
life.  They  are  usually  mixtures  of  all  three  compounds 
in  various  proportions.  Generally  one  predominates,  and 
this  to  a  large  extent  determines  the  character  of  the  fat. 
Fats  which  contain  a  large  percentage  of  olein  are  liquid  at 
ordinary  temperatures,  and  are  usually  called  oils.  Such  are 
olive  oil,  whale  oil,  cod  liver  oil.  Those  which  contain  a 


1 66     A    FOUNDATION   COURSE   IN   CHEMISTRY 

large  proportion  of  palmitin  and  stearin  are  solid.  Mutton 
fat,  beef  fat,  and  lard  are  rich  in  stearin.  Palmitin  is  so  called 
because  it  occurs  in  palm  oil,  whence  also  the  name  palmitic 
acid.  In  this  country  palm  oil  is  generally  solid. 

Glycerides  of  other  acids  often  occur  in  oils.  Thus,  drying 
oils,  such  as  linseed  oil,  hemp  oil,  poppy  oil,  contain  the 
glyceride  of  linoleic  acid,  C^K-gOg.  These  oils  resinise  on 
exposure  to  the  air,  by  oxidation.  Castor  oil  contains  the 
glyceride  of  ricinoleic  acid,  C18H34O3. 

As  vegetable  or  animal  oils  are  glycerides  and  are  saponified 
on  boiling  with  soda,  they  can  easily  be  distinguished  from 
mineral  oils,  such  as  paraffin,  vaseline,  etc.,  which  are  hydro- 
carbons, and  yield  no  soap  when  boiled  with  soda,  in  fact,  soda 
is  without  action  upon  them. 

It  will  be  noticed  that  the  formula  of  stearic  acid,  C18H;{6O2, 
and  that  of  palmitic  acid,  CuH^Og,  both  correspond  to  the 
general  formula  of  the  homologous  series,  CnH2,tO2  (p.  152),  but 
the  formula  of  oleic  acid,  C18H34O2,  does  not.  This  acid  is  not 
a  member  of  the  series.  It  contains  the  same  number  of  carbon 
atoms  as  stearic  acid,  but  lacks  two  atoms  of  hydrogen.  Oleic 
acid,  in  fact,  is  an  unsaturated  compound.  It  bears  the  same 
relation  to  stearic  acid  as  ethylene  bears  to  ethane.  This  can 
be  represented  in  their  constitutional  formulae — 

CH3— (CH2)14— CH  =  CH.COOH     Oleic  acid. 
CH3— (CH2)16— COOH     Stearic  acid. 

Like  ethylene,  oleic  acid  can  form  addition  compounds  with 
chlorine,  iodine,  etc. 

In  the  manufacture  of  soap  on  a  commercial  scale,  the  fat 
is  decomposed  with  superheated  steam — 

(C17H»COO)8Q>HB  +  3H20  ->  sQvH^COOH  +  C3H5(OH)3 
By  this  process  the  fatty  acid  itself  is  liberated.  It  is  then 
neutralised  with  soda  or  potash,  and  the  soap  produced  is  pre- 
cipitated with  concentrated  salt  solution,  in  which  it  is  insoluble. 
The  aqueous  solution  is  then  drawn  off,  and  the  glycerol,  which 
commands  a  high  price,  is  recovered  from  it.  A  certain 
amount  of  resin  is  generally  introduced  into  ordinary  soaps  to 
make  them  firmer  and  dryer. 


PARAFFINS   AND   THEIR   DERIVATIVES      167 

Transparent  soaps  are  made  by  dissolving  the  soap  in 
alcohol  and  evaporating  the  solution. 

Potash  soaps  are  called  soft  soaps.  They  are  softer  and 
more  soluble  in  water  than  soda  soaps.  When  soaps  are 
dissolved  in  water  they  undergo  partial  hydrolysis,  so  that 
they  all  show  an  alkaline  reaction  to  litmus.  Lime,  lead, 
and  other  bases  may  be  substituted  for  soda  or  potash,  but  the 
soaps  so  produced  are  insoluble  in  water.  Lead  soap  is  known 
generally  as  lead  plaster.  Ammonia  soaps  are  used  for  some 
laundry  purposes. 

The  fact  that  soaps  are  salts  of  certain  fatty  acids  provides 
an  explanation  of  the  effect  of  "hard"  water  upon  them.  As 
previously  stated  (p.  69),  such  water  usually  contains  salts  of 
calcium  and  magnesium,  and  these,  with  the  soap,  undergo  a 
double  decomposition ;  for  instance — 

CaSO4  +  2C17H35COONa  ->  Na2SO4  +  (C17H.,5COO)2Ca 

The  calcium  salt  (stearate  in  this  case)  forms  a  solid  scum 
upon  the  water.  All  the  lime  must  be  precipitated  in  this 
way  before  a  lather  can  be  produced.1 

Magnesium  salts  act  in  a  precisely  similar  manner,  but 
their  immediate  effect  on  the  soap  is  not  so  marked,  a  "  false 
lather"  being  produced  before  all  the  magnesium  is  pre- 
cipitated. It  is,  however,  temporary. 

The  "  hardness  "  of  water  caused  by  the  presence  of  mineral 
acids  (an  unusual  form  of  hardness),  is  due  to  the  decom- 
position of  the  soap  and  consequent  liberation  of  the  free 
acid — 

iG»H»COON«  +  H2SO4  ->  Na2SO4  +  2Q7H35COOH 

Isomerism. — In  studying  the  compounds  of  carbon,  we 
meet  with  many  which  are  composed  of  the  same  elements 
conbined  in  the  same  proportions  by  weight.  Such  compounds 
are  said  to  be  Isomeric.2 

Now,  if  two  or  more  compounds  consist  of  the  same 
elements  in  the  same  proportion  by  weight  and  yet  differ  in 
their  properties,  the  elements  must  be  combined  in  a  different 

1  See  note  C  at  the  end  of  this  chapter.    . 

2  Gk.  iffos,  equal  j  M6'p°s»  a  share. 


1  68     A   FOUNDATION   COURSE    IN   CHEMISTRY 

manner.  That  such  a  difference  exists  in  many  organic  com- 
pounds has  been  confirmed  by  a  multitude  of  experiments. 

If,  in  methane  (CH4),  we  replace  one  of  the  hydrogen  atoms 
by  hydroxyl  we  obtain  methyl  alcohol.  Experiment  has 
shown  that  it  does  not  matter  which  of  the  hydrogen  atoms 
is  substituted  ;  the  same  compound  is  produced  in  all  cases. 

Similarly  with  ethane  (CH:}  —  CH3),  any  one  of  the  six 
hydrogen  atoms  may  be  replaced  by  hydroxyl,  but  only  one 
ethyl  alcohol  is  produced. 

The  hydrocarbon  propane  is  C3H8,  i.e.  CH3  —  CH2  —  CHn. 
By  replacing  one  of  the  eight  hydrogen  atoms  by  hydroxyl  we 
obtain,  of  course,  propyl  alcohol,  but  now  we  find  that  instead 
of  obtaining  one  such  compound  only,  we  obtain  two,  differing 
in  their  physical  and  chemical  properties.  They  boil  at  different 
temperatures,  and  on  oxidation  produce  different  compounds. 
Careful  examination  of  these  alcohols  has  shown  that  one  of 
them  must  be  represented  by  the  formula  CH3  —  CH2  —  CH2OH, 
and  the  other  by  the  formula  CH3  .  CHOH—  CH3.  The 
first  of  these  is  normal  propyl  alcohol.  In  this  the  hydroxyl 
replaces  a  hydrogen  in  either  one  of  the  methyl  groups  (CH8). 
The  second  is  known  as  /^-propyl  alcohol  :  here  the  hydroxyl 
replaces  a  hydrogen  of  the  group  CH2. 

If  normal  propyl  alcohol  be  oxidised  it  yields  first  propyl 
aldehyde  and  then  propionic  acid  — 

/H 
CH3CH2  .  CH2OH  +  O  ->  CH3CH2  .  (X       +  H2O 


If,  however,  isopropyl  alcohol  be  oxidised  no  aldehyde  is 
formed,  but  a  compound  of  a  somewhat  different  nature  — 


3v 

>CH  .  OH  +  O  ->          )CO  +  H20  1 
CH/  CH/ 

This  compound  is  called  acetone.  It  is  the  oxygen  com- 
pound corresponding  to  the  dichlor  derivative  CH:,  .  CC12  .  CHS. 
It  is  present  in  crude  wood-spirit.  Other  similar  compounds 
are  known,  and  the  name  Ketone  is  given  to  the  class. 

1  Further  oxidation  does  not  lead  to  the  formation  of  a  corresponding 
acid. 


PARAFFINS   AND   THEIR   DERIVATIVES      169 

The  two  alcohols,  normal  propyl  alcohol  and  isopropyl 
alcohols,  are  isomeric. 

Isomerism  is,  of  course,  not  confined  to  alcohols.  Any 
class  of  compounds  may  exhibit  it,  and,  in  fact,  isomeric 
bodies  may  belong  to  totally  different  classes  of  compounds. 
All  the  paraffin  hydrocarbons  above  propane,  give  multi- 
tudinous examples  of  isomerism.  Butane,  for  example,  is 
C4H10,  and  two  compounds  of  this  formula  are  known. 
They  are  called  normal  butane  and  isobutane;  the  first 

CH,—  CH2—  CH2—  CH3,  and   the   second   ™8NcH.CHs. 

L/rlg/ 

If  now  we  replace  one  of  the  hydrogens  in  these  compounds 
by  hydroxyl  four  separate  butyl  alcohols  can  be  produced. 
(i)  From  normal  butane. 


(a)  CH3  .  CH2  .  CH2  .  CH^      CH3  .  CH2  .  CH2  .  CH2OH 

Normal  butyl  alcohol. 

(&)  CH3  .  CH2  .  CH2  .  CH3       CH3CH2CHOH  .  CH3 

Secondary  butyl  alcohol. 

(2)  From  isobutane  —  • 

(1)  CH,X  CH3X 

>CH.CH.,  >CH.CH2OH 

CH/  CH/ 

Iso  butyl  alcohol. 

(2)  CH3X  CH3X      /OH 

>CH  .  CH3  >C< 

CH/  Ctt/     XCH3 

Tertiary  butyl  alcohol. 

All   these  alcohols   are   isomeric.     They  represent   three 
classes  of  alcohols. 

(a)  Those  in  which  hydroxyl  takes  the  place  of  a  hydrogen 

atom  in  the  group  CH3  and  which  consequently 
contain  the  group  CH2OH  are  called  primary 
alcohols. 

(b)  Those   in   which  the   hydroxyl   takes  the  place  of  a 

hydrogen  atom  in  the  group  CH2,  and  which  con- 
sequently contain  the  group  CHOH,  are  called 
secondary  alcohols. 


i7o     A   FOUNDATION   COURSE   IN    CHEMISTRY 

(c)  Those  in  which  the  hydroxyl  takes  the  place  of  a 
hydrogen  atom  in  the  group  CH,  and  which  there- 
fore contain  the  group  COH  are  called  tertiary 
alcohols. 

Tertiary  alcohols  do  not  yield  either  aldehyde  or  corre- 
sponding acid  on  oxidation.  A  special  kind  of  isomerism  is 
known  as  polymerism.  This  is  found  in  the  case  of  compounds 
consisting  of  the  same  elements  in  the  proportion  by  weight, 
but  which  differ  in  their  molecular  weight.  Thus,  acetylene 
C2H2  and  benzene  C6H6  are  polymeric,  so  are  aldehyde, 
paraldehyde  (p.  150),  and  aldol  (p.  151). 

It  will  be  seen  that  isomerism  greatly  increases  the  possible 
number  of  carbon  compounds  of  all  classes. 

Carbohydrates. — Secondary  and  tertiary  alcohols  must  not 
be  confused  with  dihydric  and  trihydric  alcohols.  The  latter 
are  those  which  contain  two  and  three  hydroxyl  (OH)  groups 
respectively.  Alcohols  containing  4,  5,  and  6  hydroxyl  groups 
are  also  known.  The  last  are  called  hexahydric  alcohols. 
They  are  of  special  interest  from  the  present  point  of  view. 
It  was  shown  (p.  163)  that  the  several  hydroxyl  groups,  when 
there  is  more  than  one,  are  always  attached  to  different  carbon 
atoms. 

Hexahydric  alcohols  can,  therefore,  be  derived  only  from 
hydrocarbons  which  contain  at  least  six  atoms  of  carbon. 
The  formula  for  such  a  hexahydric  alcohol  may  therefore  be 
written — 

CH2OH  .  CHOH  .  CHOH  .  CHOH .  CHOH .  CH2OH 

Such  a  compound  is  evidently  both  a  primary  and  second- 
ary alcohol,  for  it  contains  both  the  groups  CH2OH  and  CHOH 
— it  belongs  to  both  classes. 

If  either  of  the  carbon  atoms  at  the  ends  of  the  chain  be 
oxidised  the  product,  while  still  remaining  an  alcohol,  will  also 
be  an  aldehyde.  If  any  other  of  the  carbon  atoms  be  oxidised 
the  product,  while  still  remaining  an  alcohol,  will  also  be  a 
ketone  (p.  168).  Compounds  of  both  types  are  well  known. 
They  occur  plentifully  in  fruits  and  vegetables  of  various 
kinds,  and  are  called  sugars.  The  aldehyde  type  of  sugar  is 


PARAFFINS   AND   THEIR   DERIVATIVES     171 

represented  by  glucose  (grape  sugar),  the  ketone  type  by 
fructose  (fruit  sugar).  Their  formulae  can  be  written — 

/H 
CH2OH  .  CHOH .  CHOH  .  CHOH .  CHOH  C^ 

(Glucose.)  VQ 

and 

CH2OH .  CHOH  .  CHOH .  CHOH  C^ 

(Fructose.)  \CH2OH 

It  will  be  seen  that  both  substances  can  be  represented  by 
the  empirical  formula  C6H12O6.  They  are  therefore  isomeric. 

Glucose  and  fructose  are  very  similar  in  many  respects. 
They  are  crystalline  bodies,  soluble  in  water,  of  neutral 
reaction,  have  a  sweet  taste,  and  are  easily  caramelised  (i.e. 
charred)  by  heat.1  Both  substances  are  readily  oxidised  and 
therefore  act  as  reducing  agents  towards  various  metallic  salts. 

This  is  plainly  seen  in  their  action  upon  cupric  hydroxide. 
If,  to  a  solution  of  cupric  salt,  some  caustic  soda  be  added, 
cupric  hydroxide  is  thrown  down  as  a  greenish-blue  precipitate, 
which  on  boiling  becomes  black  owing  to  its  conversion  into 
cupric  oxide.  . 

CuS04  -f  2NaOH  ->  Cu(OH)2  +  Na2SO4 
and  Cu(OH)2  ->  CuO  -f  H2O 

If,  however,  glucose  be  added  to  the  copper  sulphate  solution 
and  then  caustic  soda,  boiling  throws  down  a  red  or  yellow 
precipitate  of  cuprous  hydroxide  Cu2O,  the  cupric  hydroxide 
being  reduced  by  the  glucose  which  is  itself  oxidised.  The 
oxidation  of  glucose  by  this  method  is  somewhat  complicated 
and  leads  to  the  formation  of  several  compounds. 

For  convenience  this  reduction  of  cupric  salts  by  glucose 
and  fructose  is  done  with  Fehling's  solution,  which  is  a  mixture 
of  cupric  sulphate,  Rochelle  salt,2  and  potassium  or  sodium 
hydroxide. 

1  They  are  both  optically  active,  i.e.  they  rotate  the  direction  of  the 
vibration  of  a  beam  of  polarised  light. 

P  T-FOT-TfOOlv    1 

2  Rochelle  salt  is  potassium,  sodium,  tartrate.      CHOHCOONa  )'    I<: 

is  added,  because  tartrates  prevent  the  precipitation  of  copper  by  alkalies. 


172     A   FOUNDATION   COURSE   IN   CHEMISTRY 

Ordinary  household  sugar  (saccharose)  was  formerly 
obtained  exclusively  from  sugar  cane.  It  is  still  commonly 
called  cane  sugar,  though  large  quantities  are  now  produced 
from  sugar  beet.  The  sugar,  however,  obtained  from  sugar 
beet  is  identical,  when  purified,  with  that  obtained  from  sugar 
cane.  Its  composition  is  represented  by  the  formula  C12Ho2On. 
It  does  not  as  such  reduce  Fehling's  solution,  but  when  boiled 
with  dilute  acids  it  breaks  up  into  glucose  and  fructose — 

CuHaOn  +  H20  ->  C6H]206  +  C6H1206 

(Saccharose.)  (Glucose.)  (Fructose.) 

It  will  be  seen  that  the  cane  sugar  is  hydrolysed  in  the 
presence  of  acids.  The  change  of  saccharose  into  glucose 
and  fructose  is  thus  easily  carried  out,  but  no  means  has  yet 
been  discovered  by  which  the  process  can  be  reversed. 
Despite  this  fact,  saccharose  is  generally  regarded  as  a  com- 
pound of  glucose  with  fructose  minus  a  molecule  of  water. 

Another  sugar  of  the  empirical  formula  C^H^On  occurs  in 
milk ;  it  is  known  as  lactose.  It  is  not  so  soluble  in  water  as 
cane  sugar,  neither  is  it  so  sweet.  It  is  more  readily  decom- 
posed by  heat,  and  reduces  Fehlings  solution.  When  boiled 
with  dilute  acids  it  undergoes  hydrolysis,  but  the  products  are 
glucose  and  galactose,  Galactose 1  is  a  sugar  of  the  same 
empirical  formula  as  glucose  C6H12O6,  with  which  it  is  therefore 
isomeric. 

One  more  sugar  of  the  formula  C^H^On  is  of  importance, 
it  is  maltose.  This  is  formed  by  the  action  of  malt  on  starch. 
When  hydrolysed  it  yields  two  molecules  of  glucose. 

All  sugars  undergo  fermentation  by  the  action  of  yeast 
and  other  organisms  (p.  174),  but  it  is  probable  that  sugars  of 
the  formula  C12H22O11  undergo  hydrolytic  change  before  the 
formation  of  alcohol  from  them  can  take  place. 

The  sugars  are  merely  a  sub-division  of  a  larger  class  of 
compounds  called  carbohydrates.  This  name  owes  its  origin 
to  the  fact  that  all  the  compounds  originally  included  in  the 
group  consist  of  carbon,  hydrogen,  and  oxygen  only,  and 
the  hydrogen  and  oxygen  are  always  present  in  the  proportion 
in  which  they  are  present  in  water. 

i  Gk.  yd\a,  milk. 


PARAFFINS   AND   THEIR   DERIVATIVES     173 

Next  to  the  sugars,  the  most  important  members  of  the 
carbohydrate  group  are  starch,  cellulose,  and  dextrine.  The 
composition  of  all  these  compounds  is  represented  by  the 
empirical  formula  C6H10O5.  When  starch  is  boiled  with  dilute 
acid,  it  is  converted  into  glucose  as  shown  in  the  equation — 

C6H10O5  +  H2O  ->  C6H12O6 

A  similar  result  is  produced  by  the  action  of  diastase — 
a  ferment  which  occurs  in  malt,  and  in  smaller  quantities 
in  most  other  starchy  seeds  and  vegetables.  In  this  case  the 
starch  appears  to  be  first  converted  into  dextrine,  and,  by 
properly  regulating  the  conditions,  a  large  amount  of  dextrine 
can  be  produced  in  this  way. 

Dextrine  is  an  amorphous  substance  soluble  in  water,  and 
of  neutral  reaction.  By  the  further  action  of  diastase,  or  by 
boiling  with  dilute  acids,  it  is  converted  into  glucose.  Dextrine 
may  also  be  prepared  from  starch  by  heating  it  in  the  dry 
condition.  It  is  used  as  the  gum  on  the  backs  of  postage 
stamps. 

Several  forms  of  cellulose  are  known,  the  most  familiar  is, 
perhaps,  cotton-wool.  Good  quality  filter-paper  is  almost  pure 
cellulose.  Cellulose  is  not  changed  by  dilute  acids  to  any 
appreciable  extent,  but  strong  sulphuric  acid  converts  it  into 
glucose. 

Starch  occurs  largely  in  nearly  all  plants  and  their  seeds 
in  the  form  of  minute  grains.  It  is  chiefly  prepared  from 
various  forms  of  grain  and  from  potatoes.  Starch  grains 
vary  considerably  in  shape,  so  that  it  is  generally  possible 
to  tell  from  the  form  of  the  starch-grain  from  what  plant  the 
starch  was  obtained. 

Starch  is  insoluble  in  cold  water.  If,  however,  it  is  heated 
with  water,  the  outer  membranes  of  the  starch  cells  (grains) 
are  broken,  and  the  contents  form  a  mucilage  or  partial 
solution. 

The  usual  test  for  starch  is  provided  by  the  action  of 
iodine  upon  it.  This  forms  with  starch  a  deep  blue  coloured 
compound.  The  colour  disappears  on  warming,  but  returns 
on  cooling. 


174     A   FOUNDATION   COURSE   IN   CHEMISTRY 

Since  glucose  is  formed  from  starch,  cellulose  l  and  dextrine 
by  the  addition  of  water — that  is,  the  effect  of  the  acid — it 
might  be  expected  that  they  could  be  obtained  by  abstraction 
of  a  molecule  of  water  from  glucose,  but  no  means  is  known 
by  which  this  reverse  change  can  be  accomplished. 

Fermentation. — The  fermentation  of  glucose  by  yeast  or 
other  organisms  (p.  172),  resulting  in  the  formation  of  alcohol, 
takes  place  in  a  manner  which  can  be  represented,  in  so  far  as 
it  concerns  the  chief  products,  by  the  equation — 

C6H1206->2C2H5OH  +  2C022 

Under  the  microscope  yeast  can  be  seen  as  a  unicellular 
organism.  During  its  growth  it  often  forms  branching  chains 
of  cells.  The  fermentation  of  the  sugar  accompanies  the 
growth  of  the  yeast,  and,  therefore,  the  sugary  liquid  must 
also  contain  some  nitrogenous  material  to  supply  nitrogen 
for  the  cell  contents  of  the  organism.  Without  this  nitro- 
genous material  the  yeast  could  not  grow,  and  fermentation 
would  not  take  place.  For  this  reason  pure  sugar  solution 
does  not  undergo  fermentation.  Alcohol  is,  therefore,  to  some 
extent,  a  product  of  the  life  of  the  yeast.  It  will  not  proceed, 
indefinitely,  for  when  alcohol  has  attained  a  certain  concentra- 
tion it  arrests  the  action  of  the  organism. 

Temperature  has  also  a  great  effect  upon  the  rapidity  of 
alcoholic  fermentation.  The  most  suitable  is  about  60°  C. 

Many  other  kinds  of  fermentation  are  known ;  such  as  the 
acetic  acid  fermentation  (p.  153),  the  lactic  and  the  butyric 
acid  fermentations  (p.  178)-  They  are  all  brought  about  by 
certain  unstable  chemical  compounds  known  as  enzymes.  It 
was  formerly  the  custom  to  distinguish  two  classes  of  ferments 
— organised  and  unorganised  ;  the  former  including  yeast  and 

1  Cellulose  (cotton  wool)  when  treated  with  a  mixture  of  nitric  and 
sulphuric  acids  for  twenty-four  hours  forms  gun-cotton.      The  appearance 
of  the  cotton  is  not  appreciably  changed,  but  the  substance  has  become 
extremely  explosive.      It  is   now   cellulose  hexanitrate,   C12H14O4(NO3)6. 
Mixed  with  camphor  it  forms  the  chief  constituent  of  celluloid.    Celluloid 
is  highly  inflammable. 

2  In  the  case  of  effervescent  or  "sparkling"  wines,  etc.,  much  of  the 
fermentation  is  allowed  to  go  on  after  bottling,  so  that  the  liquid  becomes 
charged  with  carbon  dioxide  under  pressure. 


PARAFFINS   AND   THEIR   DERIVATIVES     175 

other  living  organisms,  and  the  latter  such  materials  as  diastase 
(p.  173).  It  has,  however,  been  shown  that  this  distinction  is 
scarcely  sound,  as  the  function  of  the  "  organised  ferment "  is  to 
produce  the  enzyme  which  causes  the  fermentation  to  take  place. 
Alcoholic  fermentation,  for  example,  has  been  brought  about 
by  means  of  the  expressed  juices  from  yeast,  in  the  absence 
of  living  cells.  The  juices  contain  the  enzyme,  and  fermenta- 
tion accordingly  takes  place.  It  will  not  of  course  proceed  far, 
as  the  absence  of  living  yeast  prevents  the  formation  of  fresh 
enzyme.  In  the  case  of  yeast  the  enzyme  is  known  as  zymase.1 

The  action  of  enzymes  upon  starch  is  an  important  form 
of  fermentation.  The  change  is  similar  to  that  produced  when 
the  substance  is  boiled  with  dilute  acids.  The  action  of 
diastase  on  starch  is  a  simple  example — 

C6H10O5  +  H2O  ->  C6H;2O6     Glucose. 

Other  and  perhaps  more  typical  instances  are  to  be  found 
in  the  decomposition  of  the  glucosides  (derivatives  of  glucose), 
which  occur  so  largely  in  plants.  To  bring  about  the  hydro- 
lytic  change,  a  special  ferment  (enzyme)  seems  to  be  required 
in  each  case,  but  this  always  occurs  in  the  plant  associated 
with  the  glucoside. 

The  following  are  a  few  examples  of  glucosides  and  the 
manner  in  which  they  decompose  under  the  action  of  special 
ferments. 

(a)  Salicin,  C13H18O7,  occurs  in  willow-bark.      Under  the 
action  of  an  enzyme  it  hydrolyses  as  follows  : — 

C13H1807  +  H2O  -»  C6H1206  +  C6H4OH.CH2OH 

(Salicyl  alcohol.) 

(b)  Indican,  C14H17NO6,  occurs  in  woad — 

C14H17N06  +  H20  ->  C8H7ON  +  C6H12O6 

(Indoxyl.) 

Indoxyl  is  readily  oxidised  to  indigo  blue,  (C8H5ON)2. 

(c)  Amygdaline,    CaoH^NOn,    occurs    in   bitter   almonds 
(p.  190),  also  in  the  kernels  of  peaches,  cherries,    etc.,  and 
in  the  pips  of  apples  and  pears — 

+  2H20  ->  C7H60  +  HCN  +  2C6H12O6 

(Benzaldehyde.) 
1  See  note  D  at  the  end  of  this  chapter. 


176     A   FOUNDATION    COURSE   IN   CHEMISTRY 

(d)  Saponin,    C^H^O^,   is    extracted    from    Soap    Root 
(saponaria  officinalis)  \  it  forms  a  lather  with   water  like  that 
produced  by  soap.     Mixed  with  vegetable  refuse  it  is  used  as 
a  worm-killer  on  lawns,  etc.      It   is   said  to  be  occasionally 
added  to  ginger  beer  to  produce  a  frothy  appearance.1 

(e)  Some  of  the  substances  known  as  "  tannins  "  are  also 
glucosides,  and  the  bi-hexose  sugars  (C^H^On)  may  also  be 
regarded  as  belonging  to  that  class. 

Dibasic  Acids.  —  It  was  shown  (p.  163)  that  glycol, 
C2H4(OH)2,  is  a  double  or  dihydric  alcohol.  Either  or  both 
of  the  carbon  atoms  can  be  oxidised.  In  the  latter  case  we 
obtain  a  double,  i.e.  a  dibasic,  acid  called  oxalic  acid  — 

CH2OH  COOH 

on  oxidation  becomes    | 
CH2OH  COOH 

(Glycol.)  (Oxalic  acid.) 

This  acid  is  best  prepared  by  the  action  of  concentrated 
nitric  acid  upon  sugar,  and  other  organic  materials  such  as 
starch  and  cellulose.  It  is  manufactured  on  a  large  scale  by 
heating  sawdust  with  caustic  soda  to  a  temperature  of  about 
250°  C.  In  this  case  the  sodium  salt  is  of  course  formed. 

Two  other  methods  of  formation  are  of  some  importance. 

(1)  If  a  solution  of  cyanogen  gas  (p.  179)  in  water  is  kept 
for  some  time,  it  spontaneously  undergoes  decomposition  and 
forms  ammonium  oxalate. 

CN  COONH4 

I     +  4H20  ->    | 
CN  COONH4 

(Cyanogen.) 

(2)  If  dry  carbon  dioxide  be  passed  over  metallic  sodium, 
sodium  oxalate  is  produced  — 

(COONa 


The  acid  is  generally  sold  in  crystals  containing  two 
molecules  of  water  of  crystallisation,  C2H2O4  2H2O.  It  is 
widely  distributed  in  plants,  occurring  in  several  of  the  oxalis 
varieties  (wood  sorrel,  Oxalis  acetocella\  as  the  acid  potassium 

1  See  note  E  at  the  end  of  this  chapter. 


PARAFFINS   AND   THEIR   DERIVATIVES     177 

salt.1  Calcium  oxalate  is  also  found  in  clovers  and  many 
other  plants. 

Oxalic  acid  and  its  soluble  salts  are  poisonous. 

All  substances  which  contain  the  group  (  —  COOH)  carboxyl 
have  acidic  properties.  Those  which  contain  two  such  groups 
are  dibasic.  Similar  acids  are  derived  from  propane,  butane, 
and  other  hydrocarbons.  In  fact,  there  is  a  homologous  series 
of  dibasic  acids.  Malonic  and  succinic  acid  may  be  taken 
as  examples.  The  latter  can  be  obtained  from  amber. 

/COOH  CH2COOH 

CH/  | 

\COOH  CHaCOOH 

(Malonic  acid.)  (Succinic  acid.) 

Hydroxy  Acids.—  If  only  one  of  the  carbon  atoms  in 
glycol  be  oxidised,  only  one  carboxyl  group  is  formed,  and 
the  product  is  therefore  a  monobasic  acid.  It  is  called 
glycollic  acid.  Now,  since  glycol  is  a  dihydric  alcohol,  and 
only  one  of  the  hydroxyl  groups  is  changed  into  carboxyl, 
the  other  continues  to  exist  in  the  compound,  and  cause  it  to 
exhibit  the  properties  of  an  alcohol.  In  short,  glycollic  acid 
is  at  once  an  acid  and  an  alcohol. 

On  reference  to  the  structural  formulae  it  will  be  seen  that 
glycollic  acid  is  acetic  acid  in  which  an  atom  of  hydrogen  is 
replaced  by  hydroxyl.  For  this  reason  it  is  often  called 
hydroxy-acetic  acid. 

H  H 

H—  C—  C—  OH  HO—  C—  C—  OH 

I      I!  I     II 

HO  HO 

(Acetic  acid.)  (Glycollic  acid.) 

Glycollic  acid  is  found  in  nature  in  unripe  grapes,  etc. 
Many  other  hydroxy  acids  —  both  monobasic  and  dibasic  — 
are  known.      Many  of  them  occur  in  nature,  especially    in 


1  This  salt  jcoOK  is  PrePared  artificially  and   sold  as  "Salts   of 
sorrel."     It  is  used  for  removing  inkstains,  etc. 

N 


1 78     A   FOUNDATION   COURSE   IN   CHEMISTRY 

fruits   and   in   plants   of  various    kinds.     Among    the    most 
important  is  lactic  acid,  which  is  hydroxy  propionic  acid. 

CH3CH2OH  CH3CHOH.COOH 

(Propionic  acid.)  (Lactic  acid.) 

This  substance  is  produced  by  the  fermentation  of  milk 
sugar.  The  lactose  seems  to  be  first  hydrolysed  with  the 
formation  of  glucose  and  galactose— 

Cya^Ou  +  H20  ~>  C6H]206  +  C6H]206 
These  sugars  then  undergo  decomposition — 
C6H1206->  2C2H4OH.COOH 

(Lactic  acid.) 

The  fermentation  does  not,  however,  stop  here,  but  proceeds 
to  the  formation  of  butyric  acid * — 

2C2H4OHCOOH->C3H7COOH  +  2CO2  +  2H2 

(Butyric  acid.) 

Two  hydroxy  succinic  acids  are  known.     They  are — 
CH.OH.COOH  CH.OH.COOH 

CH2COOH  CH.OH.COOH 

(Malic  acid.)  (Tartaric  acid.) 

Malic  acid  (mon-hydroxy-succinic  acid)  occurs  in  apples, 
strawberries,  and  many  other  fruits.  Tartaric  acid  (di- 
hydroxy-succinic  acid)  occurs  in  grapes,  in  berries  of  the 
mountain  ash,  and  in  other  plants.  It  can  be  made  by 
oxidising  lactose  with  nitric  acid,  but  is  generally  prepared 
from  "  argol,"  which  is  impure  potassium  hydrogen  tartrate. 
This  salt  crystallises  out  when  grape  juice  ferments.  It  is 
purified  by  recrystallisation,  and  is  then  known  as  cream  of 
tartar.2  Cream  of  tartar  is  largely  used  in  the  manufacture  of 
baking  powder. 

Only  one  tribasic  acid  need  be  mentioned.  This  is  citric 
acid.  It  occurs  largely  in  oranges,  lemons,  and  similar  fruits ; 
it  is  C3H4OH(COOH)3. 

1  Butyric  acid  is  a  liquid  which  mixes  with  water  in  all  proportions.     It 
has  an  odour  resembling  that  of  rancid  butter. 

2  Argol  is  sometimes  known  as  tartar. 


PARAFFINS   AND   THEIR   DERIVATIVES     179 

Nitrogenous  Compounds. — When  any  nitrogenous  carbon 
compound  is  heated  with  metallic  sodium,1  the  metal  combines 
with  both  the  carbon  and  the  nitrogen  and  forms  a  compound 
known  as  sodium  cyanide  (NaCN). 

Commercially,  cyanides  are  produced  from  organic  refuse 
such  as  waste  hair,  hides,  or  dried  blood,  by  fusing  them  with 
scrap  iron  and  potassium  carbonate.  The  fused  mass  is  washed 
out  with  water,  and  from  the  solution  a  crystalline  salt,  potas- 
sium ferrocyanide,2  K4FeC6N6,  may  be  easily  obtained.  This 
is  the  potassium  salt  of  hydroferrocyanic  acid,  H4FeC6N6., 
When  this  cyanide  is  heated  with  dilute  sulphuric  acid  an 
extremely  poisonous  gas,  known  as  hydrocyanic  acid  (HCN), 
is  given  off. 

It  will  be  remembered  that  when  potassium  ferrocyanide 
is  heated  with  concentrated  sulphuric  acid,  carbon  monoxide  is 
evolved. 

Hydrocyanic  acid  is  soluble  in  water,  and  the  solution  has 
an  acid  reaction.  When  neutralised  with  bases  it  forms 
cyanides— 

HCN  -f  NaOH  ->  NaCN  +  H,O 

Many  of  the  cyanides  are  soluble  in  water.  Others,  such 
as  silver  cyanide,  are  insoluble. 

If  hydrocyanic  acid  be  neutralised  with  precipitated 
mercuric  oxide,  mercuric  cyanide  is  formed.  This  substance, 
which  is  a  white  crystalline  solid,  is  decomposed  on  heating, 
yielding  mercury  and  cyanogen  gas — 

HgC2N2  ->  Hg  -f  C2N2  (cyanogen). 

This  gas  is  colourless,  and  burns  with  a  peculiar  pink- 
coloured  flame.  It  is  somewhat  soluble  in  water,  and  highly 
poisonous. 

1  Some   componnds   do   not   contain   sufficient    carbon    to    give   this 
reaction.     The  difficulty  can  be  surmounted  by  adding  a  little  sugar  to  the 
mixture. 

2  The  name  is  short  for  potassium  ferrous  cyanide,  for  the  compound 
may  be  considered  as  a  double  cyanide,  4KCN.FeC2N2,  i.e.  four  mols.  of 
potassium  cyanide  combined  with  one  mol.  of  ferrous  cyanide. 

3  Gk.,  K-UO.VOS,  blue.      The  name  cyanogen  was  given  to  the  compound 
because  many  of  its  derivatives  are  blue  in  colour. 


i8o     A   FOUNDATION   COURSE    IN    CHEMISTRY 

CEEEN 

While  cyanogen  gas  is  C2N2,  i.e.    \          ,  the  term  cyanogen 

C==N 

is    generally  given    to  the  unsaturated  group  —  C^N,  which 
often  enters  into  combination  in  organic  compounds. 

Hydrocyanic  acid  is  also  known  as  prussic  acid.  It 
contains  the  group  —  C=N,  and  its  formula  can  be  written 
H—  C=N. 

The  cyanides  are  powerful  reducing  agents.  When,  for 
instance,  potassium  cyanide  is  fused  with  red  lead  or  litharge, 
the  lead  oxide  is  reduced  to  metallic  lead  and  the  cyanide  is 
oxidised  to  cyanate  — 

KCN  +  PbO  ->  KCNO  +  Pb 

(Potassium 
cyanate.) 

From  potassium  cyanate  a  most  important  salt  can  be  ob- 
tained by  double  decomposition.  This  is  ammonium  cyanate. 
It  is  prepared  by  adding  ammonium  sulphate  to  a  solution 
of  potassium  cyanate.  From  strong  solutions  the  potassium 
sulphate  would  be  largely  precipitated,  and  the  ammonium 
cyanate  remain  in  solution.  The  ammonium  salt,  however, 
cannot  be  crystallised,  for  if  the  solution  be  allowed  to  stand 
it  gradually  undergoes  transformation.  The  change  is  more 
rapidly  brought  about  by  heating.  It  is  a  rearrangement  of 
the  elements  in  the  compound  — 

NH2\ 
NH4CNO  ->  )CO 


The  compound  produced  is  known  as  carbamide  or  urea.  It 
is  found  in  the  urine  of  all  mammals,  particularly  those  whose 
food  consists  wholly  or  partially  of  flesh.  In  fact,  it  is  the 
compound  in  the  form  of  which  the  waste  nitrogen  of  the  body 
is  chiefly  excreted.1 

The  above  preparation  of  urea  is  of  importance,  as  it 
afforded  the  first  instance  of  the  formation  in  the  laboratory 
of  a  carbon  compound  which  was  known  to  be  present  in  the 
animal  body,  and  which  was  supposed  to  be  the  product  of 

1  Uric  acid,  C5H4N4O3  (a  somewhat  complex  compound),  also  occurs  in 
urine. 


PARAFFINS   AND   THEIR   DERIVATIVES     181 

vital  force.  Since  its  preparation  in  1828,  many  other  com- 
pounds which  occur  in  plants  and  animals  have  been  prepared 
by  artificial  means,  and  "  organic  chemistry  "  no  longer  means 
the  chemistry  of  the  compounds  produced  by  organised  bodies, 
but  merely  the  chemistry  of  the  carbon  compounds. 

Cyanides  of  metals  are  not  the  only  cyanides  which  are 
known.  When,  for  instance,  methyl  potassium  sulphate, 
CH3KSO4  (p.  156),  is  heated  with  potassium  cyanide  a  simple 
reaction  takes  place  resulting  in  the  formation  of  methyl 
cyanide — 

CH3KS04  +  KCN  ->  K2SO4  +  CH3CN 

A  similar  compound  may  be  obtained  from  ethyl  compounds 
such  as  ethyl  chloride — 

C2H5C1  +  KCN  ->  C2H5CN  +  KC1 

and  in  fact  a  homologous  series  of  cyanides  can  be  obtained, 
of  which  the  first  three  members  are — 

H — C=N     .     .     .     Hydrocyanic  acid. 
CB3— C=N     .     .     .     Methyl  cyanide. 
C2H5— C=N     .     .     .     Ethyl  cyanide. 

The  importance  of  these  compounds  lies  in  the  ease  with 
which  they  undergo  hydrolysis  in  the  presence  of  caustic 
alkali— 

(i)  H.CN  -f-  2H2O->H.COONH4,  ammonium  formate; 
or,  in  the  presence  of  alkali — 

(1)  HCN  +  H2O  +  KOH  ->  H.COOK  +  NH8 

(2)  CH3CN  -KH»0  +  KOH->  CH3COOK  +  NH3 

(3)  C2H5CN  +  H20  -f  KOH  ->  C2H5COOK  +  NH3 

It  will  be  seen  therefore  that  hydrocyanic  acid,  when  hydro- 
lysed,  gives  salts  of  formic  acid ;  methyl  cyanide  gives  acetates ; 
and  ethyl  cyanide,  propionates.  For  this  reason  these  cyanides 
are  often  called  the  nitriles  of  the  acids  produced  by  hydro- 
lysis. Hydrocyanic  acid  is  formo-nitrile ;  methyl  cyanide  is 
aceto-nitrile,  etc. 

When  these  nitriles  are  treated  with  nascent  hydrogen,  i.e. 
when  hydrogen  is  liberated  in  their  solution  (by  adding  zinc 


182     A   FOUNDATION   COURSE   IN   CHEMISTRY 

and  hydrochloric  acid),  they  are  reduced  to  a  class  of  bodies 
known  as  Amines. 


<  H2.CH3 


Thus—  C      +  4H->N—  H 

III  \H 

N 

The  amines  can  also  be  prepared  by  treating  the  halogen 
derivative  of  a  hydrocarbon  with  ammonia.  When,  for 
example,  monochlorethane,  or,  preferably,  the  bromine  com- 
pound C2H5Br,  is  used,  successive  replacements  of  the  hydrogen 
in  the  ammonia  take  place,  and  four  different  compounds  are 
produced  — 

C2H5Br  +  NH3-»NH2.C2H5.HBr 
C2H5Br  +  NH2C2H5->NH.(C2H5)2.HBr 
C2H5Br  +  NH(C2H5)2->  N.(C2H5)3HBr 
C2H5Br  +  N.(C2H5)3  ->  N(C2H5)4Br 

The  compounds  produced  by  these  reactions  may  be  con- 
sidered as  ammonium  bromide,  NH4Br,  in  which  the  atoms  of 
hydrogen  are  successively  replaced  by  C2H5.  They  are  there- 
fore known  as  ethyl  ammonium  bromides.  When  treated  with 
caustic  potash  or  soda  they  behave  in  many  respects  like 
ammonium  salts  — 


NH2C2H5HBr  +  KOH->  KBr  -f  H2O  +  NH2C2H5 

Ethyl  amine. 

NH(C2H5)2HBr  +  KOH  ->  KBr  -f-  H2O  +  NH(C2H5>, 

Di-ethyl  amine. 

N(C2H5)3HBr  +  KOH  ->  KBr  -f  H2O  +  N(C2H5)3 

Tri-ethyl  amine. 

From  the  compound  N(C2H5)4Br,  a  compound  correspond- 
ing to  ammonium  hydroxide  can  be  obtained  ;  it  is  tetra  ethyl 
ammonium  hydroxide  N(C2H5)4OH. 

The  amines  are  generally  regarded  as  ammonia  in  which 
one  or  more  atoms  of  hydrogen  have  been  replaced  by  an 
equivalent  amount  of  C2H5.  Their  properties  are  very  similar 
to  those  of  ammonia.  They  are  soluble  in  water,  yielding 
akafine  solutions,  and  combine  with  acids  to  form  salts. 


PARAFFINS   AND   THEIR   DERIVATIVES     183 

Similar  compounds  can  be  prepared  having  the  same 
relationship  to  other  hydrocarbons  as  the  ethyl  amines  have 
to  ethane ;  e.g.  methyl  amines/  propyl  amines,  etc.  There  is, 
therefore,  a  homologous  series  of  each  of  the  amines,  mono, 
di,  and  tri. 

By  treatment  of  glycol  with  hydrochloric  acid,  glycol 
monochloride  (ethylene  chlorhydrin)— 

CH2OH 

CH2C1 

is  formed,  and  this  rea'cts  with  ammonia  like  ethyl  bromide, 
i.e.  the  two  substances  combine,  forming  hydroxy-ethyl 
ammonium  chloride,  from  which  hydroxy-ethylamine  may  be 
obtained  by  the  action  of  caustic  potash. 

Hydroxy-ethylamine  may  be  regarded  as  ethyl  alcohol  in 
which  an  atom  of  hydrogen  is  replaced  by  NH2,  i.e.  it  is  at 
once  an  amine  and  an  alcohol.  It  is  therefore  often  referred 
to  as  amino-ethyl  alcohol. 

Just  as  acetic  acid  is  produced  by  the  oxidation  of  ethyl 
alcohol,  so  when  the  amino  alcohol  is  oxidised,  amino-acetic 
acid  is  produced— 


CH, 


CH2NH2  CH2NH., 

I  or     CH2NH2.COOH 

2OH  COOH 

Amino  ethyl  Amino  acetic 

alcohol.  acid. 

Amino-acetic  acid  is  a  crystalline  substance,  readily  soluble 
in  water ;  it  has  both  acid  and  basic  properties,  uniting  with 
acids  to  form  salts,'  and  with  bases  to  form  other  salts,  the 
amino-acetates.  This  may  be  attributed  to  the  fact  that  the 
amino  group  NH2  is  basic,  and  the  carboxyl  group  COOH  is 
acidic. 

1  NH2CH3.  Gaseous  compound,  very  soluble  in  water,  strongly 
alkaline. 

NH(CH3)2,  di-ethyl  amine.     Gas,  easily  condensed  to  a  liquid. 

N(CH3)2,  tri-ethyl  amine.     Liquid,  b.p.  about  9°  C. 

Occurs  in  herring-brine,  also  as  the  liquids  obtained  during  the  refining 
of  beet  sugar.  The  odour  of  methyl  amine,  similar  to  that  of  ammonia, 
can  often  be  detected  in  very  large  quantities  of  beet  sugar. 


184    A   FOUNDATION   COURSE   IN    CHEMISTRY 

Amino  acetic  acid,  being  derived  from  glycol,  is  very  often 
called  glycocoll,  glycocine,  or  glycine.1  By  replacing  one  of 
the  hydrogen  atoms  of  the  CH2  group  in  the  above  formula 
by  CH3,  amino  propionic  acid2  can  be  obtained.  The  pro- 
perties of  the  amino  propionic  acids  are  very  similar  to  those 
of  glycocoll. 

The  amines  and  amino  acids  above  described  must  be 
distinguished  from  another  class  of  compounds  known  as 
acid-amides. 

When  ammonium  acetate,  CH3,  is  heated  in  the  dry  state, 
water  is  given  off  and  a  substance  known  as  acetamide, 
CH3CONH2,  is  produced— 

CH3COONH4  ->  CH3CONH2  +  H2O 

This  substance  may  be  regarded  as  ammonia  in  which  an 
atom  of  hydrogen  is  replaced  by  the  acid  radicle,  CH3CO,  or, 
better,  as  acetic  acid  in  which  the  hydroxyl  is  replaced  by  NH2. 

It  can  also  be  obtained  by  treating  an  ethereal  salt  of  acetic 
acid  with  ammonia  — 

CH3.COOC2H5  +  NH3  ->  CH3CONH2  +  QH5OH 

Acetamide  is  a  crystalline  substance  soluble  in  water,  and 
has  neither  acid  nor  basic  properties.  The  amides  of  other 
acids  may  be  prepared  in  a  similar  manner.  The  well-known 
compound  asparagine  is  the  amide  of  amino  succinic  acid  — 

CONH2 


It  is  found  in  asparagus,  peas,  beans,  etc. 

Albuminoids  and    Proteins.  —  White  of  egg,   milk  curd 
(casein),3   red   flesh   or   muscular  tissue,  skin,  etc.,  are  very 

1  A  derivative  of  amino-acetic  acid  is  largely  used  as  a  photographic 
developer,  and  is  sold  under  the  name  of  glycine.     It  is,  however,  not  the 
compound  mentioned  in  the  text  ;  it  is  para-oxyphenyl  glycine— 

CH2NHCOOH 

C6H4OH. 

2  Carbamic  acid  (p.  130)  is  amino  formic  acid. 

3  See  note  F  at  end  of  this  chapter. 


PARAFFINS   AND   THEIR   DERIVATIVES     185 

complex  substances.  Notwithstanding  the  difference  in  origin 
and  in  external  appearance,  they  are  very  similar  in  composi- 
tion, and  have  many  properties  in  common.  They  are  all 
classed  together  in  one  group,  called  albuminoids  or  proteins. 
The  average  composition  of  all  these  substances  is — 

Carbon 52*2  per  cent. 

Hydrogen 7-2  „       „ 

Oxygen 23-1  „       „ 

Nitrogen 15-8  „       „ 

Sulphur 1*7  „       „ 

1 00*0 


It  is  not  yet  known  exactly  how  the  elements  are  combined 
together,  and  their  composition  cannot  .therefore  be  indicated 
by  formulae.  On  exposure  to  air  they  become  infected  with 
bacteria,  and  are  slowly  decomposed,  giving  off  offensive  odours. 
In  the  process  of  digestion  a  somewhat  similar  series  of  changes 
occurs,  and  they  can  also  be  decomposed  by  chemical  means. 
Amongst  the  most  important  compounds  produced  in  all  these 
changes  are  amines  and  amino-acid  bodies,  such  as  glycocoll, 
etc.  It  is  believed,  therefore,  that  the  albuminoids  or  proteins 
are  complexes  of  various  amines  and  amino  acids. 


ADDITIONAL   NOTES 

A  (p.  158).  Acetylene  burnt  with  excess  of  oxygen  produces  a 
flame  of  enormously  high  temperature,  and  oxy-acetylene  blow- 
pipes are  constructed  giving  a  flame  which  can  be  used  for  piercing 
iron  or  even  for  cutting  armour  plate.  It  has  a  temperature  of 
about  3300°  C. 

B  (p.  162).  Cadmium  bromide  and  iodide  are  soluble  in  ether, 
and  hence  are  used  in  the  preparation  of  collodion  photographic 
emulsions. 

C  (p.  167).  The  cleansing  action  of  soap  is  largely  due  to  its 
power  of  forming  a  lather,  and  this  lather  is  caused  by  the  fact 
that  the  solution  of  the  soap  in  water  lowers  the  surface  tension  of 
the  liquid. 

D  (p.  175).  Yeast  contains  several  other  enzymes  besides 
zymase,  each  with  a  specific  action  which  takes  place  most  efficiently 
at  a  special  temperature.  Some,  such  as  diastase,  which  is  present 


i86     A   FOUNDATION    COURSE   IN   CHEMISTRY 

in  yeast,  invert  sugars  ;  some  cause  oxidation  (oxydase),  others 
reduce.  Zymase  is,  however,  as  far  as  is  known  at  present,  the 
only  yeast  enzyme  which  produces  alcohol. 

E  (p.  176).  Saponin  can  also  be  extracted  from  horse-chestnuts, 
quillaia  bark,  and  other  vegetable  products.  It  has  a  cleansing 
power  similar  to  that  of  soap,  and  is  of  course  unaffected  by  any 
hardness  of  the  water.  It  is  used  in  laundries  to  a  small  extent. 

F  (p.  184).  Several  important  industrial  applications  have  been 
found  for  casein.  It  is  precipitated  from  skim  milk  either  by  dilute 
sulphuric  acid  or  by  passing  sulphur  dioxide  through  the  liquid. 
The  separated  casein  is  then  used  : — 

(1)  For   sizing   paper.      For  this   purpose   it   is   dissolved   in 

ammonia  ;  water-glass  is  added  to  the  solution,  and  then 
phosphoric  acid  or  acetic  acid. 

(2)  As  glue.     For  this  it  is  mixed  with  a  quarter  of  its  weight 

of  water  and  a  little  sodium  bicarbonate. 

(3)  As  a  food  stuff. 

(4)  For  paints.     It  is  mixed  with  about  one-fifth  of  its  weight 

of  quicklime  and  the  necessary  colouring  matter. 

(5)  As  artificial  horn  or  ivory.     The  purified  casein  after  being 

dried  is  treated  with  formalin  and  again  dried  ;  it  is  then 
very  hard  and  tough.  It  can  be  moulded  when  hot,  and 
cut  or  turned  on  the  lathe  when  cold. 


CHAPTER   XV 

COAL   TAR 

THIS  substance,  which  has  already  been  mentioned  as  a  bye- 
product  in  the  manufacture  of  coal  gas  (p.  121),  is  the  most 
important  source  of  a  large  number  of  carbon  compounds 
many  of  which  are  of  vast  importance  in  the  arts  and  industries, 
and  also  in  medicine. 

it  is  a  very  complex  mixture.  Upwards  of  150  different 
compounds  have  been  separated  from  it,  and  so  great  is  the 
industrial  value  of  the  most  important  of  them,  that  the  coal 
tar  is  worth  as  much,  if  not  more,  than  the  coal  gas  which  used 
to  be  the  only  material  kept  from  the  destructive  distillation  of 
coal. 

The  utilisation  of  coal  tar  and  of  the  ammoniacal  liquor 
obtained  during  this  process  provides,  therefore,  a  convincing 
object  lesson  in  the  value  of  the  study  of  bye-products  and 
"  waste  "  materials. 

A  ton  of  coal  of  high  quality  will  produce  about  10,000 
cubic  feet  of  coal  gas,  and  somewhat  more  than  10  gallons  of 
tar ;  also  ammonia  liquor  sufficient  for  the  preparation  of  about 
30  Ibs.  of  ammonium  sulphate. 

The  coal  tar  is  generally  subjected  to  fractional  distillation. 
The  distillates  are  known  commercially  as  (i)  light  oils  (the 
distillate  obtained  below  170°  C.)j  (2)  carbolic  oils  (between 
170°  and  230°);  (3)  creosote  oils  (2^o°-2'jo0)  j  (4)  anthracene 
oil  (above  270°).  The  residue  is  a  black  solid  known  as 
pitch. 

Each  of  the  oils  can  be  further  separated.  From  the  light 
oils  we  obtain,  by  more  careful  distillation,  a  series  of  important 


1 88     A   FOUNDATION   COURSE   IN   CHEMISTRY 

compounds,  of  which  the  most  valuable,  benzene,  distils  over  in 
an  almost  pure  condition. 

This  compound  is  the  first  of  a  series  of  hydrocarbons 
quite  as  important  as  the  paraffins.  It  is  represented  by  the 
formula  C6H6,  and  various  considerations  determine  that  its 
constitution  is  best  represented  in  the  form  of  a  ring — 

H 


H—  C      C—  H 

II        I 
H—  C       C—  H 


H 

By  replacement  of  one  of  the  hydrogen  atoms  by  methyl, 
etc.,  other  members  of  the  series  can  be  formed.  The  first 
three  are  — 

C6H6  C6H5CH3,  U  C7H8  C6H5C2H5,  i.e.  C8H10 

Benzene.  Toluene.  Xylene. 

The  general  formula  for  the  series  is  CnH2rt_e.  It  is  known 
as  the  series  of  the  aromatic  hydrocarbons. 

Benzene  l  is  a  colourless  volatile  liquid  boiling  at  8o'5°  C. 
Its  odour  is  not  unpleasant.  It  is  highly  inflammable,  and 
burns  with  a  luminous  flame.  It  is  largely  used  as  a  solvent 
of  fats  and  oils,  and  is  therefore  employed  in  removing  grease 
stains,  etc. 

Benzene  and  its  related  hydrocarbons  differ  greatly  in  their 
properties  from  the  paraffins. 

The  paraffins,  for  example,  are  not  affected  by  concen- 
trated sulphuric  acid.  If  benzene,  however,  be  treated 
with  concentrated  sulphuric  acid,  benzene  sulphonic  acid  is 
formed  — 

C6H6  +  H2S04  ->  C6H5HS03  +  H2O 

1  This  must  not  be  confused  with  benzine,  which  is  a  light  paraffin  oil, 
Benzene  is  often  called  Benzol. 


COAL  TAR  189 

This  substance  forms  salts  with  bases  known  as  benzene- 
sulphonates.  The  potassium  salt  is  C6H5KSO3.  When  this 
salt  is  fused  with  caustic  potash  "  carbolic  acid  "  is  produced— 

C6H5KS03  +  KOH  ->  K2S03  +  C6H5OH 
"  Carbolic  acid  "  (C6H5OH)  is  not  really  an  acid  ;  it  is  the 
mono  hydroxyl  derivative  of  benzene,  more  closely  allied  to 
alcohols  than  to  acids.     It  is  known  as  phenol. 

Phenol  is  a  colourless  crystalline  substance,  soluble  with 
difficulty  in  water,  and  miscible  with  alcohol  and  ether  in  all 
proportions.  It  has  a  peculiar  characteristic  odour,  and  is 
used  largely  as  a  disinfectant.  Its  poisonous  properties, 
however,  necessitate  care  in  using  it. 

Again,  the  paraffins  are  not  attacked  by  nitric  acid,  but 
benzene  is  nitrated.  If  benzene  be  mixed  with  concentrated 
sulphuric  acid  and  nitric  acid,  and  the  mixture  kept  cool 
nitro  benzene  is  formed  — 

C6H6  -f  HNO3^C6H5NO2  -f  H2O 

(The  sulphuric  acid  is  added  to  remove  water  and  prevent 
reversal  of  the  reaction.) 

Nitro-benzene,  like  most  nitro-compounds,  is  yellow  in 
colour.  It  is  a  liquid,  boiling  at  205°.  It  has  an  odour 
similar  to  that  of  bitter  almonds,  and  is  therefore  sometimes 
used  for  imitating  this  odour,  particularly  in  perfuming  common 
soaps,  etc.  Commercially  it  is  known  as  oil  of  mirbane. 

Nitro-benzene  is  prepared  on  a  large  scale  for  conversion 
into  aniline.  This  change  is  brought  about  by  reduction, 
generally  by  nascent  hydrogen  — 


C6H5NOa  +  6H  ->  CeHsNHg  +  2H2O 

Aniline. 

Aniline  is  a  colourless  oily  liquid  which  becomes  brown 
on  exposure  to  the  air.  It  is  slightly  soluble  in  water,  to 
which  it  imparts  a  faint  alkaline  reaction. 

As  will  be  seen  from  its  formula,  aniline  has  the  same 
relation  to  benzene  as  ethyl  .  amine  has  to  ethane  ;  it  is,  in 
fact,  amino  benzene.  It  forms  salts  with  acids  as  the  amines 
do.  Aniline  sulphate  is  C3H5NH3HSO4,  and  the  acetate 
CH3COOC6H5NH3. 


i9o     A   FOUNDATION   COURSE    IN    CHEMISTRY 

Like  ammonium  acetate,  aniline  acetate  undergoes  change 
on  being  gently  heated,  yielding  acetanilide.1 

CH3COOC6H5NH3->  C6H5NHCOCH3  -f  H2O 

The  second  of  the  hydrocarbons,  toluene,  C6H5CH3,  on 
being  treated  with  chlorine  gas  in  the  presence  of  sunlight, 
yields,  among  other  compounds,  benzyl  chloride,  C6H5CH2C1, 
and  this,  on  being  boiled  for  a  long  time  with  water,  has  its 
chlorine  replaced  by  hydroxyl,  forming  C6H5CH2OH.  The 
compound  formed  is  benzyl  alcohol.2  On  oxidation  it  yields 
an  aldehyde  called  benzaldehyde,  a  cdmpound  which  occurs 
in  bitter  almonds,  laurel  leaves,  etc.  Its  formation  from 
amygdalin  is  given  on  p.  175.  Commercially,  benzaldehyde 
(benzoic  aldehyde)  is  made  from  bitter  almonds.  These  may 
supply  two  per  cent,  of  their  weight,  and  owing  to  this  method 
of  preparation  it  is  known  as  oil  of  bitter  almonds.  It  is 
a  liquid  of  a  pleasant  odour,  scarcely  soluble  in  water,  and 
boiling  at  179°  C.  It  is  not  poisonous,  and  is  used  largely  as 
a  flavouring  material. 

Its  formation  from  benzyl  alcohol  is  expressed  in  the 
equation — 

C6H6CH2OH  +  O  -»  C6H5COH  4-  H2O 

On  exposure  to  the  air  benzaldehyde  readily  undergoes 
oxidation,  forming  benzoic  acid,  C6H5COOH.  This  compound 
occurs  in  gum  benzoin,  in  Peru  balsam  and  Tolu  balsam,  and, 
combined  with  glycocine  (aminoacetic  acid)  in  the  urine  of 
horses,  cows,  or  other  herbivorous  animals.3  Benzoic  acid 
forms  lustrous  crystals  which  are  fairly  easily  dissolved  by  hot 
water.  When  heated  with  lime  or  other  alkali  benzoic  acid 
yields  benzene — 

C6H5COOH  -f  CaO  ->  CaCO3  -f  C6H6 

1  Acetanilide  is  used  in  medicine  under  the  name  of  "  Antifebrine." 

2  It  will  be  remembered  that  a  primary  alcohol  always  contains  the 
group  CH2OH.     Benzyl  alcohol  is  therefore  a  primary  alcohol. 

3  The  actual  compound  present  is  hippuric  acid.     This  compound  on 
being  boiled  with  hydrochloric  acid  undergoes  hydrolyis — 

C9H?N03  +  H20->C6H5COOH  +  CH2NH2COOH 
Hippuric  acid.  Glycocine. 


COAL   TAR  191 

An  important  acid  is  obtained  by  causing  the  substitution 
of  one  of  the  hydrogen  atoms  of  the  group,  C6H5  (phenyl),  by 
hydroxyl.  The  acid  is  C6H4OHCOOH,  and  is  known  as 
salicylic  acid.  It  is  found  as  the  methyl  ester  in  oil  of  Winter- 
green,  which  owes  its  odour  to  the  presence  of  this  compound. 

It  can  be  prepared  by  treating  phenol  with  carbon  tetra 
chloride  and  alcoholic  caustic  potash,  or  more  easily  by  treating 
the  methyl  salicylate  obtained  from  oil  of  winter  green  with 
caustic  potash.1 

Salicylic  acid  is  used  as  an  antiseptic  and  as  a  food 
preservative.2 

On  being  heated  with  lime  or  an  alkali  it  yields  phenol — 

C6H;OHCOOH  +  CaO  ->  CaCOa  +  C6H5OH 

From  the  carbolic  oils,  the  second  distillate  in  the  separation 
of  coal  tar,  naphthalene  can  be  obtained.  This  compound  has 
the  formula  C10H8.  It  is  largely  used  as  an  insecticide.  It 
possesses  a  peculiar  characteristic  odour,  and  is  a  white 
crystalline  solid,  melting  at  about  79°  C. 

Many  other  compounds  may  be  obtained  from  benzene,  but 
they  do  not  come  within  the  scope  of  this  work. 

1  The  process  of  decomposing  an  ester  with   an  alkali   is  known  as 
saponification,  from  its  analogy  to  the  decomposition  of  fats  by  caustic 
alkalies  and  the  resulting  formation  of  soap. 

2  Salicylic  acid  is  a  drug  with  strongly  marked  properties,  and  therefore 
its  use  as  a  preservative  cannot  be  recommended. 


CHAPTER  XVI 

SOME   COMMON    METALS 

THE  term  "  metal "  is  applied  to  a  large  group  of  elements 
possessing  those  well-known  and  easily  recognisable  properties 
which  are  familiar  to  us  in  the  case  of  silver,  lead,  gold,  iron, 
etc.  These  properties  are  :  a  peculiar  sheen,  which  for 
want  of  a  more  explanatory  term  is  called  a  "  metallic  "  lustre, 
malleability  and  ductility,  or  the  capability  of  being  hammered 
or  rolled  into  thin  leaves,  and  of  being  drawn  into  wire,  and 
high  conductive  power  towards  heat  and  electricity. 

The  metals  also  generally  form  basic  oxides,  and  can  take 
the  place  of  hydrogen  in  acids  forming  salts. 

It  may  be  convenient  to  divide  the  metals  into  two  main 
groups  as  follows  :— 

I.  Light  metals,  including — 

(a)  The  alkali  metals  :  potassium,  sodium,  lithium,  etc. 

(b)  The  metals  of  the  alkaline  earths :  calcium,  strontium, 

barium,  and  magnesium. 

(c)  The  earth  metals  :  aluminium,   and  certain  very  rare 

elements. 

II.  Heavy  metals  (those  with  a  specific   gravity  greater 
than  5),  including — 

(a)  The   iron    group :   iron,   manganese,    nickel,    cobalt, 

chromium,  zinc,  cadmium. 

(b)  The  copper  group  :  copper,  lead,  mercury,  silver. 

(c)  The  noble  metals  :  gold  and  platinum. 

(ct)  Other  metals :   antimony,  bismuth,   tin,  and   possibly 

arsenic. 
The  scope  of  this  book  will  not  allow  of  a  full  description 


SOME   COMMON    METALS  193 

of  these  elements.    Some,  however,  are  of  such  great  importance 
that  the  student  must  become  familiar  with  at  least  their  most 
important  properties. 
The  Light  Metals. 

(a)  The  Alkali  Metals. — These  form  basic  oxides  soluble 
in  water,  i.e.  alkalies. 

Sodium. — This  metal  and  its  compounds  have  already 
been  described  (p.  80). 

Potassium. — This  element  is  very  similar  to  sodium  in 
most  of  its  properties,  but  is  more  chemically  active.  Its 
more  important  compounds  have  already  been  described 

(P-  97). 

(b)  The  Metals  of  the  Alkaline  Earths.— These  metals  form 
oxides  of  an  earthy  nature,  slightly  soluble  in  water,  to  which 
they  impart  an  alkaline  reaction. 

Calcium  (p.  65). 

Barium. — The  most  plentiful  minerals  containing  barium 
are  barytes  (heavy  spar),  BaSO4,  and  witherite,  BaCO3.  A 
solution  of  barium  chloride,  BaCU,  is  largely  used  in  the 
laboratory  as  a  test  for  sulphates,  as  barium  sulphate  is  an 
extremely  insoluble  salt,  and  is  therefore  precipitated  whenever 
barium  chloride  is  added  to  the  solution  of  a  sulphate. 

Barium  sulphate  is  used  in  the  preparation  of  permanent 
white  paint,  as  it  does  not  blacken  in  impure  air.  Barium 
peroxide  is  used  in  the  commercial  preparation  of  oxygen 
(p.  19). 

Magnesium. — This  metal  is  widely  distributed  in  nature. 
It  is  found  as  magnesite,  MgCO3,  and  in  larger  quantities  as 
dolomite  or  magnesian  limestone,  MgCO3CaCO3.  The  sul- 
phate and  chloride  are  also  found,  and  magnesium  chloride 
and  bromide  occur  in  sea-water. 

The  metal  is  usually  obtained  by  the  electrolysis  of  fused 
carnallite,  MgCl2KC16H2O.  It  is  white  like  silver,  somewhat 
tough,  and  keeps  fairly  well  in  the  air.  It  burns  when  heated, 
giving  a  light  of  great  brilliancy  and  rich  in  chemically  active 
rays,  so  that  it  is  often  used  in  photography.  The  compound 
formed  on  burning  magnesium  in  air  is  chiefly  oxide,  but  a 
small  quantity  of  nitride,  Mg3Ns,  is  also  produced  (magnesium 

0 


194     A   FOUNDATION   COURSE   IN   CHEMISTRY 

combines  directly  with  nitrogen).  Magnesium  acts  invariably 
as  a  divalent  element.  It  is  rapidly  acted  upon  by  acids, 
forming  the  corresponding  salt  and  liberating  hydrogen. 
This  is  true,  even  in  the  case  of  nitric  acid,  if  the  acid  be 
sufficiently  dilute.  When  magnesium  is  dissolved  in  hydro- 
chloric acid,  the  chloride  is  formed.  This  salt  can  be  ob- 
tained in  deliquescent  crystals  of  the  composition  MgCl26H2O 
from  the  solution.  If,  however,  the  crystals  are  heated,  the 
salt  undergoes  hydrolysis,  the  oxide  or  a  basic  chloride  being 
formed — 

MgCl2  +  H20  ->  MgO  +  2HC1 

Magnesium  sulphate  is  the  substance  well  known  as 
Epsom  salts,  it  generally  occurs  crystallised  with  seven  molecules 
of  water  of  crystallisation,  MgSO47H2O.  Magnesium  carbonate 
occurs  in  nature,  but  if  an  alkaline  carbonate  be  added  to  a 
solution  of  a  magnesium  salt,  a  white  precipitate  is  thrown 
down  and  carbon  dioxide  is  liberated.  This  precipitate  is  no 
pure  magnesium  carbonate,  but  a  mixture  of  carbonate  and 
hydroxide  in  varying  proportions.  It  is  used  in  medicine 
after  it  has  been  washed  and  dried  at  a  low  temperature ;  it  is 
known  as  "magnesia  alba."  All  the  salts  of  magnesium, 
except  the  phosphate,  are  soluble  in  a  solution  of  ammonium 
chloride,  owing  to  the  formation  of  double  salts. 

(c)  The  Earth  Metals. — The  only  metal  of  this  group 
which  is  at  all  common  is  aluminium. 

Ahiminium  is  one  of  the  most  plentiful  elements  in  the 
crust  of  the  earth ;  it  is  a  constituent  of  most  of  the  common 
rock-forming  minerals. 

The  oxide  of  aluminium  (alumina),  A12O3,  is  an  earthy 
powder  when  prepared  artificially,  but  occurs  as  a  mineral  in 
various  forms.  The  commonest  variety  is  emery  or  corundum, 
a  substance  only  slightly  less  hard  than  the  diamond.  Ruby 
and  sapphire  are  also  aluminium  oxide  coloured  with  other 
metallic  oxides.1 

Aluminium  oxide  forms  salts  with  acids,  and  also  with  strong 

1  In  the  ruby  the  colouring  matter  is  a  trace  of  chromium  ;  while 
sapphire  is  coloured  with  cobalt. 


SOME   COMMON    METALS  195 

bases  (aluminates).  The  metal  is  soluble  in  hydrochloric 
and  sulphuric  acids,  and  in  caustic  soda  or  potash  (p.  61). 

When  it  is  dissolved  in  sulphuric  acid,  aluminium  sul- 
phate is  formed,  A12(SO4)3.  This  sulphate  forms  important 
double  salts  with  the  sulphates  of  the  alkalies,  the  most 
important  being  that  with  potassium  sulphate.  This  is  known 
as  alum,  and  has  the  composition  shown  by  the  formula, 
Al2(SO4);iK2SO424H2O.  Several  double  salts  of  this  nature  are 
known,  and  the  term  "alum"  is  applied  to  them  all.  They 
contain  the  sulphate  of  a  monovalent  metal  or  of  ammonia, 
and  the  sulphate  of  a  trivalent  metal,  together  with  twenty-four 
molecules  of  water.  They  all  crystallise  in  the  same  form,  i.e. 
they  are  isomorphous. 

The  most  important  alums  are — 

(1)  K2SO4Al2(SO4)324HoO.     Common  alum. 

(2)  Na2SO4Al(SO4)324H2O.     Sodium  alum. 

(3)  (NH4)2SO4A12(SO4)324H2O.     Ammonium  alum. 

(4)  K2SO4Cr2(SO4)324H2O.     Potassium  chromium  alum. 

(5)  Na.2SO4Cr2(SO4)324H2O.     Sodium  chromium  alum. 

(6)  (NH4)2SO4Cr2(SO4)324H2O.       Ammonium     chromium 

alum. 

(7)  K2SO4Fe2(SO4)324H2O.     Potassium  iron  alum. 

(8)  Na2SO4Fe2(SO4)324H2O.     Sodium  iron  alum. 

(9)  (NH4)2SO4Fe2(SO4)324H2O.     Ammonium  iron  alum. 
The  sodium  alums  do  not  crystallise  easily. 
Aluminium    salts    are   used  as   "  mordants " l   in   dyeing. 

Their  use  is  due  to  the  fact  that  colloidal  alumina  combines 
with  certain  colouring  matters  to  form  insoluble  coloured 
compounds.  In  dyeing,  these  compounds  are  formed  in  the 
fabric  to  be  dyed,  and  as  they  are  insoluble,  the  colour  is  fixed, 
i.e.  not  easily  washed  out.  These  insoluble  compounds  of  a 
dye  with  a  colloidal  hydroxide  are  known  as  lakes.2  The 
colour  produced  depends  not  only  upon  the  dye,  but  also 
upon  the  mordant.  Aluminium  salts  are  also  used  in  tanning 
leather. 

1  Lat.  mordere,  to  bite.     Salts  of  iron,  chromium,  and  tin  are  used  for 
a.  similar  purpose. 

2  French,  laqne,  lac, 


196     A   FOUNDATION    COURSE    IN    CHEMISTRY 

The  chief  ore  of  aluminium  is  bauxite,  which  is  chiefly 
alumina.  From  this  ore  the  metal  is  obtained  by  electrolysis, 
the  oxide  being  dissolved  in  fused  cryolite,  Na3AlFt;. 

Aluminium  is  a  nearly  white  metal  of  low  specific  gravity 
(27);  it  keeps  bright  in  dry  air,  but  is  quickly  tarnished  by 
water,  especially  by  salt  water.  It  is  not  acted  on  by  nitric 
acid,  nor  by  the  vegetable  acids.  It  can,  therefore,  be  used 
for  cooking  utensils,  but,  if  it  is  so  used,  care  must  be  taken 
that  alkalies  such  as  soda  are  not  brought  into  contact 
with  it.  It  is  also  appreciably  acted  on  by  common  salt. 

The  Heavy  Metals.— (Sp.  gr.  over  5.) 

Iron. — The  chief  compounds  occurring  in  nature  are 
the  oxides,  Fe2O;;  haematite,  Fe2(OH)0limonite,  FeaO4  magnetite 
(so  called  because  many  specimens  of  this  mineral  have 
magnetic  properties),1  and  a  carbonate  FeCO:i  (spathic  iron 
ore).  These  constitute  the  ores  of  iron.2  -The  carbonate 
of  iron  is  often  found  mixed  with  clay,  when  the  mineral  is 
known  as  clay  iron  stone.  It  often  contains  organic  material 
which  makes  it  very  dark  in  colour  (black  band  iron  stone). 

The  chemical  process  of  obtaining  iron  from  its  ores 
(smelting)  is  a  very  simple  one.  Whatever  form  of  ore  is 
used,  it  is  first  turned  into  the  oxide  by  roasting  in  the  air;  it 
is  then  reduced  in  a  furnace,  by  carbon  in  the  form  of  coke  or 
small  coal.  The  carbon  removes  the  oxygen  from  the  iron 
oxide,  and  forms  large  quantities  of  carbon  monoxide.  This 
gas,  until  comparatively  recently,  was  allowed  to  escape  and 
burn  at  the  top  of  the  blast  furnace,  but  it  is  now  led  off  and 
burned  in  a  suitable  "  stove  "  in  such  a  manner  as  to  heat  the 
air  blast  which  passes  into  the  furnace,  thereby  saving  a  large 
expenditure  of  fuel.  As,  however,  many  of  the  ores  of  iron 
contain  impurities  of  a  siliceous  and  infusible  nature,  limestone 
is  always  placed  in  the  furnace  with  the  iron  ore  and  coal  or 
coke.  This  combines  with  the  siliceous  material  to  form  a 
fusible  "  slag  "  of  a  nature  somewhat  similar  to  glass.  The 
metal  when  run  out  from  the  furnace  is  generally  cast  into 

1  It  is  the  substance  which  was  known  as  "  lode  stone." 

2  An  ore  is  a  naturally  occurring  compound  which  is  used  as  a  source 
of  a  metal, 


SOME   COMMON   METALS  197 

bars  about  three  feet  long  and  six  inches  thick;  these  are 
known  as  "  pigs." 

Iron  is  placed  upon  the  market  in  three  forms :  wrought 
iron,  cast  iron;  and  steel.  Of  these,  wrought  iron  is  the 
purest.  It  is  a  dark  grey  metal  with  brilliant  metallic  lustre, 
and  a  specific  gravity  of  7*7.  Its  melting-point  is  extremely 
high  (about  1600°  C.);  but  in  order  to  work  it,  it  is  not  neces- 
sary to  raise  its  temperature  to  anything  like  this  extent. 
Long  before  melting,  wrought  iron  becomes  soft  almost  like 
wax,  and  can  in  this  condition  (at  about  600°  C.)  be  pressed, 
hammered,  or  rolled  into  any  required  shape.  It  can  also  be 
welded,  that  is,  two  pieces  of  the  metal  can  be  caused  to  unite 
when  hammered  or  rolled  together.1 

Steel  is  iron  which  contains  from  0*8  to  2*5  per  cent,  of 
carbon,  in  combination  with  the  iron  as  iron  carbide,  but 
is  otherwise  as  pure  as  can  be  produced.  Wrought  iron 
is  tough  and  not  very  hard,  and  when  heated  and  suddenly 
cooled  these  properties  do  not  undergo  any  appreciable 
change;  but  the  presence  of  carbon  in  the  iron  greatly 
increases  its  hardness,  and  lowers  its  melting-point,  so  that 
steel  is  liquid  at  about  1400°  C.,  and  can  be  cast.  Steel, 
however,  softens  before  it  melts,  and  can,  therefore,  like 
wrought  iron,  be  forged;  such  treatment  toughens  the  steel 
and  causes  it  to  become  fibrous,  whereas  cast  steel  consists 
of  fine  crystalline  grains.  Continual  knocking  or  vibration 
may  cause  forged  steel  to  revert  to  its  crystalline  condition 
and  become  brittle.2 

A  most  important  property  of  steel  is  its  power  of  being 
tempered,  or  rendered  soft  or  hard  at  will.  In  order  to  make 
steel  assume  any  required  degree  of  hardness,  it  is  first  of  all 
made  red  hot,  and  then  cooled  suddenly  by  plunging  it  into 
cold  water  or  mercury.  With  the  latter  material  it  becomes 
so  hard  that  it  will  cut  glass — it  is  said  to  be  "  glass  hardened." 

1  A  few  other  metals  possess  the  property  of  welding,  the  chief  being 
platinum,  which  can  be  welded  at  a  red  heat,  and  gold,  which  can  be 
Avelded  even  when  cold.     Lead  may  also  be  included  among  the  weldable 
metals. 

2  The  axles  of  railway  carriage  wheels  have  been   known    to   break 
after  much  use,  owing  to  this  change  in  structure. 


198     A   FOUNDATION   COURSE   IN   CHEMISTRY 

The  metal  is  then  put  upon  a  "  hot  plate  "  and  carefully 
heated.  As  heated  iron  oxidises  readily  in  the  air,  a  film  of 
oxide  is  soon  formed  on  the  surface.  This  varies  in  colour 
with  its  thickness,  first  appearing  as  a  pale  straw  colour  at 
about  220°  C.,  and  then  passing  through  various  shades  of 
orange,  purple,  violet,  and  blue,  to  grey.  The  higher  the 
temperature  to  which  the  hardened  steel  is  heated  the  softer  it 
becomes.  A  skilful  workman  can  tell  by  the  colour  of  the 
metal  approximately  what  temperature  has  been  reached,  and 
can  stop  the  heating  when  the  desired  condition  has  been 
attained.  Thus  tools  for  steel  engraving  are  only  allowed  to 
reach  the  straw-coloured  stage  (about  221°  C.),  while  springs 
and  wood  saws  are  heated  until  the  colour  of  the  film  of  oxide 
is  almost  grey  (just  below  300°  C.). 

In  the  manufacture  of  steel  from  iron  containing  phosphorus, 
the  converter  is  lined  with  a  mixture  containing  lime  and 
magnesia,  which  absorbs  the  phosphoric  oxide  produced  during 
the  process,  and  forms  basic  calcium  phosphate.  When  the 
lining  has  absorbed  all  the  phosphorus  it  can  take  up,  it  is 
removed,,  and  when  pulverised  is  sold  as  a  phosphatic  fertiliser. 
It  is  called  "  basic  slag."  It  is  not,  however,  a  slag  in  the  usual 
sense,  as  it  is  not  a  fusible  material. 

If  the  amount  of  carbon  is  increased  to  4  or  5  per  cent,  the 
melting-point  of  the  metal  becomes  still  lower ;  the  metal  also 
loses  its  toughness  and  is  crystalline  and  somewhat  brittle.  It 
is  now  known  as  cast  iron.  There  are  two  kinds  of  cast  iron, 
grey  and  white. 

White  cast  iron  has  the  greater  part  of  its  carbon  combined 
with  the  iron,  it  is  obtained  by  rapidly  cooling  the  melted  metal. 
On  slowly  cooling,  some  of  the  carbon  separates  as  minute 
crystals  of  graphite,  which  impart  a  grey  colour  to  the 
metal. 

All  kinds  of  iron  oxidise  readily  in  moist  air,  even  at 
ordinary  temperatures,  forming  impure  Fe(OH);$  (iron  rust). 
When  heated  strongly,  oxidation  quickly  takes  place,  and  the 
compounds  Fe3O4  and  Fe^.O^  are  produced. 

Owing  to  the  rusting  of  iron  in  moist  air  at  a  low  tempera- 
ture, and  to  the  fact  that  the  rust  formed  does  not  adhere  to 


SOME   COMMON   METALS  199 

the  metal,  it  is  necessary  to  protect  the  iron  from  the  action  of 
the  atmosphere.  This  is  often  done  by  covering  it  with  a 
coating  of  paint,  or  it  is  galvanised  (p.  204),  tinned  (p.  212),  or 
nickel-plated  (p.  203).  For  a  similar  protective  purpose,  iron 
which  has  to  be  heated  is  often  covered  with  a  coating  of 
black  lead  (graphite). 

When  iron  is  treated  with  dilute  sulphuric  or  hydrochloric 
acid,  hydrogen  is  evolved,1  and  a  salt  of  iron  formed  in  which 
one  atom  of  iron  takes  the  place  of  two  atoms  of  hydrogen. 

Fe  +  H2SO4  ->  FeSO4  -f  H2 
Fe  -f-  2HC1  ->  Fed,  +  H2 

Such  salts  are  known  as  tenons  salts.  They  form  green 
crystals  containing  water  of  crystallisation.  Ferrous  sulphate 
is  the  most  familiar  of  these ;  it  has  been  known  for  a  very  long 
time  under  the  names  of  green  vitriol,  copperas,  etc.,  and  has 
been  largely  used  in  the  making  of  writing  ink.2  When  exposed 
to  the  air,  the  ferrous  salts  are  slowly  oxidised,  a  change  which 
can  be  brought  about  more  quickly  by  the  action  of  an  oxidis- 
ing agent  such  as  nitric  acid  or  potassium  permanganate. 

(1)  Fed,  +  HC1  +  HNO,  ->  FeCl3  -f-  H2O  -f  NO2 

(2)  ioFeSO4  +  8H2SO4  -f  2KMnO4 

->  5Fe2(S04)3  +  K2S04  +  2MnSO4  +  4H8O 

(Ferric  sulphate.) 

In  these  reactions  the  salts  FeCl3  and  Fe2(SO4)3  are  formed, 
and  in  them  the  iron  is  obviously  trivalent.  They  are  known 
as  ferrzV  salts.  Ferric  salts  are  usually  yellow  in  colour,3  so 
that  the  oxidation  of  the  ferrous  salt  by  nitric  acid  is  accom- 
panied by  a  change  in  the  colour  of  the  solution  from  green  to 
yellow  or  brown. 

1  The  hydrogen  thus  obtained  is  always  impure,  owing  to  the  presence 
of  compounds  of  carbon  and  hydrogen  formed  by  the  action  of  the  acid 
upon  the  iron  carbide  contained  in  the  metal. 

2  Ink  is  formed  from  ferrous  sulphate  by  adding  a  solution  of  gallic 
acid  to  a  solution  of  the  salt.     It  is  owing  to  the  iron  that  ink  contains 
that  ink  stains  on  linen  often  develop  into  the  rusty-brown  quarks  known 
as  "  iron-mould."     These  consist  of  deposits  of  ferric  oxide  in  the  fibres  of 
the  material.     Ink  stains  can  be  removed  by  a  solution  of  oxalic  acid  or 
"  Salts  of  Sorrel  "  (KHC204). 

3  Iron  alum,  which  is  a  ferric  salt,  forms  pale  violet  crystals. 


200     A   FOUNDATION   COURSE   IN   CHEMISTRY 

If  a  solution  of  caustic  soda  or  potash  or  of  ammonia  be 
added  to  a  solution  of  a  ferrous  salt  a  greenish  precipitate  is 
produced  which  rapidly  turns  brown  on  exposure  to  the  air. 
If  a  perfectly  pure  ferrous  salt  be  used,  and  the  precipitation 
carried  out  in  the  absence  of  air,  the  solid  thrown  down  is 
nearly  white  ;  it  is  ferrous  hydroxide — 

FeSO4  +  2NaOH  ->  Na2SO4  +  Fe(OH)2 

The  oxidation  to  Fe(OH)a  causing  the  brown  colour  may  be 
represented  thus— 

2Fe(OH)a  +  HaO  +  O  -»  2Fe(OH), 

Ferrous  sulphate  FeSOa.  7H2O  (green  vitriol)  was  used  for 
preparing  fuming  sulphuric  acid.  For  this  purpose  the  salt 
was  first  roasted  in  the  air,  whereby  it  became  converted  into 
basic  ferric  sulphate — 

2FeSO4  +  H2O  +  O  -»  2FeSO4(OH) 
and  this  on  being  heated  decomposed — 

2FeSO4(OH)  ->  Fe2O3  +  H2SO4  -f  SO, 

and  the  resulting  mixture  of  sulphuric  acid  and  sulphur  trioxide 
was  collected  and  sold  as  fuming  oil  of  vitriol  (p.  91). 

Iron  combines  with  sulphur  when  heated  (p.  3),  forming 
ferrous  sulphide.     This   compound  can  also  be  obtained  by 
adding  ammonium  sulphide  to  a  solution  of  an  iron  salt. 
(i.)  Ferrous  salt — 

FeS04  +  (NH4)2S  ->  FeS  +  (NH4),SO4 
(ii.)  Ferric  salt — 

2FeCl8  +  3(NH4)2S  ->  2FeS  +  6NH4C1  +  S 
The  sulphide  Fe2S3,  corresponding  to  the  oxide  FeaO3,  is  not 
known. 

The  following  are  some  of  the  chief  compounds  of  iron  in 
common  use  : — 

Ferric  oxide,  Fe2O3.     Polishing  material,1  jewellers'  rouge. 
Colouring  material,  Venetian  red. 

1  Ferric  oxide  was  known  to  the  later  alchemists  as  "  Crocus  Martis," 
as  thex  element  iron  was  generally  referred  to  by  the  name  of  Mars,  with 
which  planet  it  was  supposed  to  be  very  closely  connected. 


SOME   COMMON    METALS  201 

Ferric  hydroxide,  Fe(OH)y.  Pigment  (Mars  orange,  etc.). 
Also  used  as  an  antidote  in  cases  of  arsenical  poisoning. 

Ferrous  sulphate,  FeSO4 .  7H2O.  (Green  vitriol.)  Used  in 
the  making  of  writing  ink  (p.  199,  note). 

Ferric  ferrocyanide,  Fe'"[Fe"(CN)6]3.  Used  as  a  pigment 
under  the  name  of  Prussian  blue. 

Manganese. — This  is  a  reddish-grey,  lustrous  metal,  obtained 
from  its  oxide  by  reduction  with  aluminium.  It  melts  at  a 
higher  temperature  than  iron,  and  is  readily  dissolved  by  acids, 
even  acetic  acid,  with  evolution  of  hydrogen  and  formation 
manganous  salts.  These  salts  are  generally  crystalline  sub- 
stances, pink  in  colour. 

One  of  the  most  familiar  compounds  of  manganese  is  the 
dioxide  MnO2,  which  occurs  as  a  natural  mineral  and  is  then 
known  as  pyrolusite.  Manganese  dioxide  will  dissolve 
in  cold  concentrated  hydrochloric  acid  without  evolution 
of  chlorine  (p.  79),  forming  a  dark  brown-green  liquid.  If 
water  be  added  to  this  liquid  the  hydrated  dioxide  is  again 
thrown  down.  This  is  due  to  the  formation  of  a  tetrachloride 
(MnQ4),  which  is  decomposed  by  water  (hydrolysed)— 

MnCl4  +  4H2O  ->  Mn(OH)4  +  4HC1 

If  the  dark  brown-green  solution  be  boiled  it  rapidly 
becomes  nearly  colourless  and  loses  chlorine.  The  reaction 
for  the  preparation  of  chlorine  in  this  manner  may  be  therefore 
represented  as  taking  place  in  two  stages — 

(1)  MnO,  +  4HC1  ->  MnCl4  +  2H2O 

(2)  MnCl4  -»  MnCl2  +  C12 

There  are  several  oxides  of  manganese  :  MnO,  obtained  as 
the  hydrate  (Mn(OH)2)  by  adding  an  alkali  (caustic  soda)  to  a 
manganous  salt;  Mn3O4,  Mn2O;(,  MnO2,  MnO;{,  and  Mn2O7. 
Of  these  MnO  and  Mn2O;!  are  basic  oxides,  the  former  giving 
rise  to  manganous  salts  and  the  latter  to  manganic  salts.1 
The  oxides  MnO3  and  Mn2O7  are  acidic  and  give  rise  to 
salts  known  as  manganates  and  permanganates. 

The  soluble  manganates  are  green,  the  permanganates  are 

1  Manganic  salts  are  unstable  in  the  presence  of  water. 


202     A   FOUNDATION   COURSE   IN   CHEMISTRY 

bright  violet  in  solution.  The  most  familiar  permanganates  are 
those  of  sodium  and  potassium.  They  are  powerful  oxidising 
agents  and  are  used  as  disinfectants,  the  solution  of  sodium 
permanganate,  NaMnO4,  being  largely  sold  under  the  name  of 
"  Condy's  Fluid." 

The  oxidising  power  of  permanganates  is  utilised  in  many 
ways.  A  very  important  application  in  the  chemical 
laboratory  is  the  estimation  of  ferrous  salts  (p.  199), 
oxalic  acid,  hydrogen  peroxide,  etc.  In  all  these  cases  the 
oxidation  is  made  to  take  place  in  the  presence  of  sul- 
phuric acid,  and  the  permanganate  is  reduced  to  a  manganous 
salt — 

2KMnO4  +  5C2H2O4  +  sH2SO4 

->  K2SO4  +  2MnSO4  +  ioCO2  +  8H.O 

In  the  presence  of  sulphuric  acid  five-eighths  of  the  oxygen  in 
a  permanganate  is  available  for  oxidation. 

Manganese  dioxide,  MnO2,  may  also  act  as  a  weak  acidic 
oxide,  and  a  compound  CaMnO3  is  formed  from  the  manga- 
nous chloride  left  after  the  preparation  of  chlorine,  as  a  means 
of  recovering,  the  manganese  dioxide,  for  this  compound 
(calcium  manganite)  will  liberate  chlorine  from  hydrochloric 
acid — 

CaMnO3  +  6HCl->  CaCL  +  MnCl2  +  Cla 

Manganese  dioxide  is  also  used  in  colouring  porcelain. 
Alone,  it  imparts  a  violet  tint ;  in  the  presence  of  a  little  iron 
the  colour  obtained  is  brown.  In  the  manufacture  of  glass 
it  is  also  added  to  remove  the  green  tint  which  would  be 
imparted  by  small  quantities  of  ferrous  iron.  This  it  does 
partly  by  oxidising  the  iron  to  the  ferric  condition.  Ferric 
salts  would  colour  the  glass  yellow,  but  the  colour  is  much 
feebler  than  the  green  imparted  by  ferrous  salts,  and  therefore 
the  glass  is  left  almost  colourless.  Moreover,  any  yellow 
colour  is  counteracted  by  the  violet  which  the  manganese 
would  give  alone,  an  imperceptible  neutral  tint  being  pro- 
duced. Glass  thus  decolorised  with  manganese  slowly  turns 
violet  on  exposure  to  bright  sunlight. 


SOME   COMMON   METALS  203 

In  addition  to  the  manganese  compounds  already  enume- 
rated, manganese  borate  is  of  some  importance.  It  is  placed 
on  the  market  as  a  brown  powder  and  is  used  in  the  prepara- 
tion of  varnish,  as  a  very  small  quantity  added  to  linseed  oil 
(p.  1 66)  causes  the  oil  to  absorb  oxygen,  resinise,  and  to 
harden  much  more  rapidly. 

Nickel. — The  metal  is  familiar,  as  it  is  often  used  as  a 
protective  covering  for  iron,  upon  which  it  is  deposited  by 
the  electric  current.  The  iron  is  then  said  to  be  nickel  plated. 
The  alloy  of  nickel  with  zinc  and  copper  is  known  as  German 
silver. 

The  nickelous  salts  are  apple  green  in  colour  when 
crystallised ;  the  commonest  is  the  sulphate,  NiSO46H2O. 

Cobalt. — This  metal  is  similar  to  nickel  in  its  chemical 
properties.  Its  oxide,  CoO,  is  chiefly  used  in  colouring  glass, 
to  which  it  imparts  a  fine  blue  colour.  Various  blue  pigments 
(smalt,  cobalt  blue,  etc.)  are  silicates  of  a  glassy  nature,  reduced 
to  a  very  fine  powder. 

Cobaltous  salts  are  pink  when  they  contain  water  of 
crystallisation,  but  are  blue  when  anhydrous. 

Chromium. — A  metal  which  has  received  its  name  from 
the  variety  of  colours  which  its  compounds  display. 

Chromium  itself  is  a  bright,  pale  grey,  very  hard  metal,  of 
very  great  infusibility  (it  melts  at  a  temperature  of  about 
3000°  C.).  It  is  dissolved  by  hydrochloric  acid  and  sulphuric 
acid,  and  assumes  the  passive  state *  when  treated  with  con- 
centrated nitric  acid. 

It  forms  chromic  salts  in  which  the  metal  is  trivalent 
(chromic  sulphate  is  Cr2(SO4)3) ;  these  salts  are  either  green  or 
violet  (chrome  alum,  p.  195) ;  and  chromous  salts  in  which  it  is 
divalent.  Chromous  chloride,  CrCL2,  is  bright  blue  in  colour ; 
chromous  acetate  is  chocolate  red. 

Chromium  also  forms  an  acidic  oxide,  CrO3,  which  yields, 

1  The  "  passive "  state  is  also  assumed  by  iron.  Both  iron  and 
chromium  after  being  dipped  in  very  concentrated  nitric  acid,  no  longer 
dissolve  in  acids.  This  change  in  properties  is  supposed  to  be  due  to  the 
formation  of  a  thin  coating  of  difficultly  soluble  oxide.  A  sharp  blow 
causes  the  metal  to  resume  its  active  condition,  not  only  at  the  point  where 
it  is  struck,  but  over  the  entire  surface. 


204    A   FOUNDATION   COURSE   IN   CHEMISTRY 

with  water,  chromic  acid,  H2CrO4.  The  salts  are  known  as 
chromates  and  are  either  yellow  or  red;  they  are  powerful 
oxidising  agents.  Potassium  chromate,  K2CrO4,  and  potassium 
dichromate,  K2Cr2O7,  i.e.  K2CrO4.CrO3,  are  perhaps  the  most 
important. 

Chromic  oxide,  Cr2O^,  is  a  green  substance  largely  used  as 
a  pigment. 

Zinc.—  This  metal  occurs  in  nature  as  sulphide,  ZnS  (zinc- 
blende),  and  also  as  carbonate  (calamine)  and  silicate. 

It  is  a  pale  grey,  somewhat  soft  metal  which  melts  at 
420°  C.  It  is  largely  used  not  only  in  a  pure  state  but  also  in 
many  alloys  (p.  216).  It  finds  an  important  application  in 
art  castings,  as  it  is  fairly  cheap,  and  can  easily  be  coloured 
externally  to  look  like  bronze. 

It  is  also  used  for  coating  iron  plates,  which  are  then 
known  as  "  galvanised  "  iron  ;  this  name  arose  from  the  fact 
that  the  zinc  was  originally  deposited  upon  the  iron  by  an 
electric  current;  now,  however,  the  iron  plates  are  merely 
dipped  in  molten  zinc.  Zinc-covered  iron  should  not  be  used 
for  drinking  vessels,  as  the  zinc  is  somewhat  easily  attacked  by 
moist  air,  and  the  compounds  formed  are  poisonous. 

Zinc  as  fine  turnings  or  thin  foil  burns  in  the  air  with  a 
bluish-green  flame  forming  zinc  oxide 

It  forms  but  one  series  of  salts  and  in  these  it  is  divalent. 
Many  of  them  can  be  obtained  by  dissolving  the  metal  in  the 
corresponding  acid,  when  hydrogen  is  liberated  and  the  salt 
produced.  If  zinc  is  absolutely  pure,  it  is  almost  insoluble  in 
acids.  Contact  with  a  small  piece  of  another  metal  such  as 
platinum  or  copper,  however,  causes  the  solution  of  the  zinc 
with  the  liberation  of  hydrogen  at  the  surface  of  the  other 
metal.  The  same  effect  may  be  brought  about  by  adding  a 
small  quantity  of  a  solution  of  a  salt  of  silver,  copper,  or  lead. 
In  this  case  the  zinc  replaces  the  metal  in  its  salt — 

Zn  +  CuSO4  ->  ZnSO4  -f  Cu 

thereby  bringing  the  zinc  in  contact  with  metallic  copper  or 
other  metal. 

Zinc  oxide  can  be  obtained  from  the  salts  of  zinc  by  the 


SOME   COMMON    METALS  205 

addition  of  the  solution  of  an  alkali.  A  white  flocculent 
precipitate  is  thrown  down  ;  this  is  zinc  hydroxide — 

ZnSO4  +  2NaOH->Zn(OH)2  +  Na.2SOs 

• 
If  the  zinc   hydroxide  be   filtered   off,   washed   and   heated 

strongly,  it  loses  its  water  and  becomes  converted  into  zinc 
oxide.  Should,  however,  an  excess  of  caustic  alkali  be  added, 
the  precipitate  of  zinc  hydroxide  dissolves.  This  is  due  to 
the  formation  of  a  soluble  salt  in  which  the  zinc  oxide  acts  in 
an  acidic  manner. 

Zn(OH)2  +  2NaOH  ->  Na2ZnO2  +  2H2O 

(Sodium  zincate.) 

Zinc  oxide  is  often  used  as  a  white  pigment  under  the 
name  of  zinc  white ;  it  is  also  used  in  medicine. 

Precipitated  zinc  sulphide,  which  is  also  white,  is  similarly 
used  in  the  preparation  of  white  paints.  It  is  obtained  when 
ammonium  sulphide  is  added  to  a  solution  of  a  zinc  salt. 

Zinc  sulphate  (white  vitriol),  ZnSO47H2O,  is  a  white  crystal- 
line salt  easily  soluble  in  water. 

Cadmium. — A  metal  very  similar  to  zinc  in  its  chemical 
properties,  and  often  found  in  small  quantities  in  zinc  ores. 
It  is  a  pale  bluish-grey  metal  nearly  as  soft  as  lead. 

Cadmium  sulphide,  CaS,  is  used  as  a  pigment  under  the 
name  of  cadmium  yellow. 

Copper. — This  is,  industrially,  one  of  the  most  important  of 
the  metallic  elements.  It  occurs  native,  and  for  this  reason,  it 
has,  together  with  gold  and  silver,  been  known  from  a  very 
early  period.  It  is  characterised  by  its  bright  rose-red  colour. 
This  colour  is,  however,  only  seen  in  fresh  surfaces,  for  in 
a  short  time  the  metal  becomes  covered  with  a  film  of  oxygen 
or  sulphur  compounds,  which,  without  at  first  destroying  the 
metallic  lustre,  impart  to  the  metal  the  brown-red  colour 
usually  known  as  "  copper-red." 

The  chief  compounds  of  copper  which  occur  in  nature  are 
copper  pyrites,  CuFeS2,  malachite  (a  basic  carbonate  of  copper), 
Cu(OH)2CuCO3,  and  cuprite  or  ruby  copper  ore,  Cu2O. 

The  metal  has  a  specific  gravity  of  8'8;  it  is  tough, 
tenacious,  malleable,  and  ductile. 


206     A   FOUNDATION    COURSE   IN    CHEMISTRY 

It  is  largely  used  for  utensils  of  all  kinds,  and  owing  to  the 
fact  that  it  can  be  beaten  into  any  required  shape  it  finds 
application  for  ornamental  and  artistic  purposes. 

It  is  also  occasionally  used  for  roofing,  although  when 
exposed  to  moist  air  it  gradually  becomes  covered  with  a 
green  layer  consisting  of  oxygen  compounds  and  basic  car- 
bonate, which,  however,  never  becomes  very  thick. 

Its  high  conductivity  for  the  electric  current — it  is  inferior 
to  silver  only  in  this  respect — causes  it  to  be  extensively  used 
in  electrical  engineering.  Telephone  and  telegraph  wires  are 
invariably  made  of  it. 

When  copper  is  heated  to  a  red  heat  it  combines  fairly 
rapidly  with  oxygen,  the  oxide  forming  black  scales  on  the 
metal,  which  fall  off  and  leave  a  fresh  surface  for  oxidation. 

Copper  is  not  easily  attacked  by  any  dilute  acid  with  the 
exception  of  nitric  acid.  Hot  concentrated  sulphuric  acid 
dissolves  it  (p.  86).  Nitric  acid  readily  attacks  it,  the  gaseous 
products  of  the  reaction  varying  with  the  strength  of  the  acid 
(p.  136). 

Copper  forms  two  basic  oxides  and  two  series  of  salts, 
cupric  and  cuprous^  of  which  the  cupric  are  the  more  stable 
under  ordinary  conditions.  In  these,  the  copper  is  divalent, 
while  in  the  cuprous  salts  it  is  probably  monovalent. 

When  copper  is  dissolved  in  nitric  acid,  a  blue  solution  is 
formed  which  on  evaporation  at  a  moderate  temperature  leaves 
blue  crystals  of  cupric  nitrate,  Cu(NO3)23H2O. 

If  to  a  solution  of  copper  nitrate  caustic  soda  is  added,  a 
bright  blue  gelatinous  precipitate  is  thrown  down;  this  is 
cupric  hydroxide,  Cu(OH)2.  On  boiling,  the  precipitate  loses 
water  and  also  its  blue  colour,  being  converted  into  a  heavy 
black  precipitate  of  cupric  oxide,  CuO.  If  the  hydroxide 
or  oxide  be  treated  with  other  acids  the  corresponding  cupric 
salt  is  formed. 

The  most  important  cupric  salts  are  : — 

(i)  Cupric  sulphate,  CuSO4.  This  compound  when  an- 
hydrous is  a  yellowish  white  solid,  but  it  is  more  often  seen 
combined  with  water  as  CuSO45H2O  (blue  stone  or  blue 
vitriol).  This  salt  has  a  limited  application  in  agriculture. 


SOME   COMMON    METALS  207 

Bordeaux  mixture,  used  as  a  fungicide,  is  made  by  mixing 
copper  sulphate  with  slaked  lime. 

(2)  Cupric  chloride,  CuCU.  2H.2O,  can  be  obtained  as  blue 
crystals,  the  anhydrous  salt  is  yellow. 

Ctiprous  Salts.  —  If  cupric  chloride  be  boiled  with  copper 
and  concentrated  hydrochloric  acid,  a  dark  liquid  is  obtained, 
which  on  being  poured  into  water  throws  down  white  crystals 
of  cuprous  chloride,  CuCl.  The  same  compound  is  obtained 
when  sulphur  dioxide  is  passed  into  a  solution  of  cupric  chloride. 
Cuprous  chloride  is  insoluble  in  water  and  is  readily  oxidised 
to  a  cupric  compound  on  exposure  to  the  air. 

If,  again,  a  solution  of  potassium  iodide  be  added  to  a 
solution  of  a  cupric  salt,  ciiprous  iodide  is  obtained  as  a 
white  precipitate,  coloured  brown  by  liberated  iodine  — 

2CuSO4  +  4KI  ->  2CuI  +  2K2SO4  +  I2 

Cuprous  oxide  is  easily  obtained  by  treating  a  cuprous  salt 
with  a  caustic  alkali,  but  the  student  is  more  likely  to 
become  acquainted  with  it  in  testing  for  glucose  (p.  171). 

Other  compounds  of  copper  which  are  of  importance  are  — 
(i)  Cupric  acetate  :  this  salt  can  be  obtained  in  blue- 
green  crystals  by  dissolving  cupric  hydroxide  in  acetic  acid 
and  crystallising  the  solution.  If,  however,  copper  is  exposed 
to  the  air  in  contact  with  dilute  acetic  acid,  basic  cupric 
acetate  is  formed  — 


This  compound  is  known  as  verdigris. 

By  treating  it  with  arsenious  acid  and  acetic  acid 

(2)  Cupric  arsehio-acetate   is   produced  as  a   light-green 
solid   of    peculiarly   brilliant    tint.     This   is   Paris   green   or 
emerald  green  ;  it  is  largely  used  as  a  pigment. 

Its  formula  is  Cu(C2H3O2)2Cu3As2O6. 

(3)  Scheele's  green  is  CuHAsO3;  it  has  been  used  as  a 
green  pigment,  but  the  poisonous  nature  of  this  and  emerald 
green  limit  their  use  considerably.      Both   of  the  materials, 
however,  are  used  occasionally  as  fungicides  and  insecticides. 

Cupric  salts  can  easily  be  detected  in  solution  by  the  deep 


208     A    FOUNDATION    COURSE   IN    CHEMISTRY 

blue  colour  produced  by  ammonia,  due  to  a  compound  of  the 
copper  salt  and  the  ammonia.  Thus  copper  sulphate  forms 
Cu(NH3)4SO4.HoO,  which  can  be  obtained  from  the  solution 
by  addition  of  alcohol,  in  which  it  is  insoluble.  These 
deep  blue  compounds  have  the  power  of  dissolving  cellu- 
lose, and  their  solutions  have  been  used  for  "  water-proofing" 
paper. 

Towards  both  animal  and  vegetable  life,  copper  salts 
generally  act  as  powerful  poisons. 

Lead. — This  is  another  metal  of  high  industrial  importance. 
It  is  found  in  nature  chiefly  as  sulphide,  (PbS),  galena,  and  as 
carbonate  (PbCO3),  cerussite. 

The  many  uses  of  the  metal  depend  chiefly  upon  its  low 
melting-point,  326°  C.,  its  great  density  (sp.  gr.  1 1*4),  and  its  soft- 
ness. It  is  used  either  alone  or  alloyed  with  other  metals 
(p.  216).  Sheet  lead  is  used  for  roofing;  lead  foil  forms  an 
airtight  package  for  tea,  and  lead  pipes  are  often  employed  to 
carry  the  water  supply  to  houses.  There  is,  however,  some 
danger  in  the  use  of  lead  water-pipes,  unless  the  water  be 
hard.  Hard  water  will  generally  cover  lead  with  a  coating  of 
carbonate  which  is  insoluble,  and  which  protects  the  metal 
from  further  action.  Soft  water,  however,  containing  little 
or  no  carbonate  but  having  oxygen  in  solution,  causes  the 
formation  of  lead  hydroxide  which  is  perceptibly  soluble. 
Lead  thus  dissolved  in  water  acts  as  a  powerful  poison. 
Cases  of  lead  poisoning  produced  by  water  which  has  passed 
through  lead  pipes  are  not  uncommon.  The  danger  is 
removed  by  coating  the  inside  of  the  pipes  with  tin.  Lead 
forms  a  series  of  oxides.  They  are  Pb2O,  PbO,  Pb3O4,  Pb2O3, 
PbO2.  Of  these  the  most  important  are  the  following  : — 

Lead  Monoxide,  PbO. — This  is  prepared  in  two  forms ; 
a  yellowish-red  crystalline  substance  obtained  by  direct 
oxidation  of  lead,  known  as  litharge;  a  yellow  powdery 
variety  made  by  heating  lead  nitrate  or  carbonate,1  known 
as  massicot.  Lead  monoxide  is  used  in  glass-making,  for 
preparing  salts  of  lead,  and  in  the  manufacture  of  drying  oils. 

1  All  the  other  oxides  of  lead  are  converted  into  massicot  on  being 
heated  strongly  in  the  air. 


SOME   COMMON   METALS  209 

It  is  a  basic  oxide,  but  can  act  as  a  feeble  acidic  oxide  with 
strong  bases. 

Red  Lead,  Minium,  Pb3O4,  may  be  formed  by  carefully 
heating  litharge  in  the  air.  It  is  a  substance  of  a  bright  red 
colour,  and  has  been  employed  for  a  very  long  time'  as  a  pig- 
ment.1 When  treated  with  nitric  acid  it  yields  lead  peroxide 
and  lead  nitrate. 

Pb3O4  +  4HNO,->  PbO2  +  2Pb(NO3)2. 

Lead  Peroxide,  PbOa. — A  dark-brown  powder  which  readily 
evolves  oxygen  on  heating. 

The  salts  of  lead  are  generally  insoluble  in  water,  the  chief 
exceptions  being  the  acetate  and  the  nitrate.  The  acetate  has 
an  extensive  industrial  use.  It  has  a  sweet  taste  (it  is  very 
poisonous),  and  is  therefore  known  as  sugar  of  lead. 

White  Lead  is  a  mixture  of  basic  carbonates.  It  is  prepared 
by  the  action  of  carbon  dioxide  upon  lead  oxide.  Several 
methods  are  employed,  the  most  common  at  the  present  time 
is  that  of  grinding  lead  oxide  with  lead  acetate  and  water  and 
passing  carbon  dixoide  through  the  mixture. 

It  is  largely  used  for  making  white  paint;  it  has  a  great 
advantage  over  all  other  white  paints  in  its  much  greater 
opacity  and  covering  power.  The  disadvantages  attending 
its  use  have,  however,  led  to  the  substitution  of  other  white 
materials  (ZnO,  ZnS,  BaSO4,  etc.),  for  all  lead  compounds  very 
readily  turn  black  in  air  containing  traces  of  sulphuretted 
hydrogen,  the  blackening  being  caused  by  the  formation  of 
lead  sulphide,  PbS.2 

Lead  Chromate,  PbCrO4,  is  used  as  a  yellow  pigment  under 
the  name  of  chrome  yellow.  On  being  warmed  with  caustic 
soda  a  basic  lead  chromate  is  formed,  which  is  of  a  dark  orange 
tint  and  is  known  as  chrome  red.  Various  mixtures  of  these 

1  Red-lead  mixed  with  linseed  oil,  etc.,  is  used  in  making  gas-tight 
joints  with  gas  pipes.     The  substance  assists  the  resinisation  of  the  oil. 

2  Paint  which  has  been  blackened  in  this  manner  can  generally  be 
made  white  again  by  the  application  of  hydrogen  peroxide,  which  oxidises 
the  sulphide  to  sulphate — 

PbS  +  4H,O,  ->  PbSO4  +  4H2O 

P 


210     A   FOUNDATION    COURSE    IN   CHEMISTRY 

two  compounds  are  employed  to  give  different  tints  of  orange 
and  yellow.  The  chrome  yellow  is  easily  prepared  by  adding 
potassium  chromate  or  bichromate  to  a  solution  of  lead  acetate 
in  water. 

Mercftry. — This  is  the  only  metal  which  is  liquid  at  the 
ordinary  temperature.  It  is  largely  employed  in  making 
barometers,  thermometers,  and  other  scientific  instruments. 
It  is  a  bright,  lustrous  metal  of  great  density  (sp.  gr.  13 -5 9), 
and  boils  at  a  temperature  of  358°  C.  It  remains  untarnished 
in  the  air  at  ordinary  temperature  indefinitely,  but  if  heated  for 
a  long  time  to  about  300°  C  it  becomes  covered  with  red  scales 
of  mercuric  oxide  (p.  15). 

The  most  important  compounds  of  mercury  are  mercuric 
sulphide  (HgS).  This  forms  the  commonest  ore  of  mercury, 
cinnabar.  Artificially  prepared,  mercuric  sulphide  is  the 
red  pigment  known  as  vermilion.1  Mercuroiis  chloride^  HgCl, 
long  known  under  the  name  of  calomel,2  is  used  to  some 
extent  in  medicine.  Memiric  chloride^  HgCl2,  is  used  as  an 
antiseptic.  It  is  known  as  corrosive  sublimate.  All  the  salts 
of  mercury  are  poisonous. 

Mercury  forms  alloys,  known  as  amalgams,  with  many 
metals,  some  of  which  have  industrial  application. 

Silver. — This  metal  has  been  known  from  the  earliest 
times,  as  it  occurs  free  in  nature.  This  and  the  manner  in 
which  it  resists  oxidation  in  the  air  either  cold  or  when  heated, 
its  fine  whiteness,  and  its  brilliant  lustre  when  polished,  have 
caused  it  to  be  used  in  all  ages  for  articles  of  ornament  and  for 
coinage.  It  melts  at  about  945°  C.,  and  although  oxygen  does 
not  combine  with  it  at  ordinary  pressure  even  when  the  silver 
is  melted,  yet  the  metal  absorbs  this  gas  to  the  extent  of  about 
twenty-two  times  its  own  volume,  and,  on  solidifying,  gives  it 
out  again,  so  that  the  surface  of  silver  which  has  been  melted 

1  When   sulphuretted   hydrogen   is  passed   through  a   solution   of  a 
mercuric  salt  a  black  precipitate  of  mercuric  sulphide  is  thrown  down ; 
on  treatment  with  a  solution  of  an  alkali  sulphide  the  black  precipitate 
gradually  turns  red,  owing  to  the  formation  of  the  crystalline  red  form  of 
mercuric  sulphide. 

2  Gk.  KaAos,  beautiful  ;  /xeAos,  black.     It  forms  a  black  substance  with 
ammonia.     This  substance  contains  free  mercury. 


SOME   COMMON    METALS  211 

and  cooled  is  always  pitted  with  apertures  from  which  the 
oxygen  has  escaped. 

Silver  is  not  attacked  by  dilute  acids  except  nitric  acid, 
but  this  easily  dissolves  it,  forming  silver  nitrate.  Concen- 
trated sulphuric  acid  also  dissolves  it,  forming  silver  sulphate 
and  liberating  sulphur  dioxide.  The  metal  is  easily  acted 
upon  by  sulphuretted  hydrogen  and  many  other  sulphur  com- 
pounds. Thus  silver  spoons  become  blackened  from  contact 
with  the  albumen  of  egg  (this  contains  sulphur),  and  silver 
articles  in  the  pocket  will,  if  in  contact  with  indiarubber  or 
vulcanite,  such  as  the  handle  of  a  fountain-pen,  become  black 
from  the  sulphur  which  these  materials  contain.  In  all  cases 
the  blackening  is  caused  by  the  formation  of  a  film  of  silver 
sulphide,  Ag2S. 

Silver  forms  but  one  series  of  salts  in  which  it  is  mono- 
valent.  That  most  easily  obtained  is  the  nitrate,  which  readily 
crystallises  in  anhydrous  crystals  from  the  solution  obtained  by 
dissolving  silver  in  nitric  acid.  The  salt  is  often  fused  and 
cast  in  sticks  for  medical  use,  as  it  acts  as  a  strong  caustic.  It 
often  goes  by  the  name  of  "  Lunar  caustic,"  from  " Luna"  the 
moon,  the  name  applied  to  silver  by  the  mediaeval  alchemists. 
From  the  solution  of  the  nitrate,  soluble  chlorides  precipi- 
tate the  very  insoluble  white  silver  chloride,  AgCl.  This  salt, 
together  with  the  bromide  and  iodide,  has  wide  application  in 
photography,  owing  to  the  fact  that  light  causes  a  change  in  its 
colour.  Under  the  influence  of  light,  silver  chloride  slowly 
becomes  violet  in  tint.  All  silver  salts  are  more  or  less 
affected  by  light  in  this  way,  the  change  being  greatly  assisted 
by  the  presence  of  traces  of  oxidisable  matter.  Most  of  the 
salts  of  silver  are  soluble  in  ammonia  solution. 

The  Noble  Metals. — Gold  and  platinum  are  remarkable  for 
the  fact  that  they  occur  in  nature  almost  entirely  in  the  native 
condition.  Both  are  unacted  upon  by  all  acids  except  the 
mixture  of  hydrochloric  and  nitric  acids  known  as  aqua  regia 
(p.  80).  This  dissolves  them  and  forms  the  chlorides. 

Gold  has  for  ages  been  used  for  personal  ornament  and  for 
coinage.  It  is  a  heavy  soft  yellow  metal  (sp.  gr.  19*3);  it 
melts  at  1035°  C.  Its  malleability  is  remarkable ;  it  may  be 


*i*     A   FOUNDATION   COURSE   IN   CHEMISTRY 

rolled  or  beaten  out  into  leaves  so  thin  as  to  transmit  light  (the 
light  so  transmitted  is  greenish).  These  leaves  are  used  under 
the  name  of  gold-leaf  for  surface  decoration. 

As  gold  is  so  soft,  it  is  usually  alloyed  with  copper  for  both 
jewellery  and  coinage,  and  is  thereby  rendered  somewhat  more 
red  in  tint.  Coinage  from  the  Australian  mint  at  Sydney  is, 
however,  alloyed  with  silver,  and  is  therefore  of  a  very  pale 
yellow  colour.  The  only  salt  of  importance  is  the  chloride, 
AuCl3;  on  being  heated  it  loses  its  chlorine  and  leaves  metallic 
gold. 

Platinum  chloride,  PtCl4,  decomposes  in  the  same  way  and 
leaves  platinum  in  the  form  of  a  black  powder  known  as 
platinum  sponge  (p.  88).  Platinum  chloride  has  an  important 
application  in  the  estimation  of -the  element  potassium,  a  double 
chloride  of  potassium  and  platinum  being  formed  when  the 
salts  are  mixed.  This  double  chloride  is  insoluble  in  alcohol. 

The  metal  may  be  easily  precipitated  from  the  solutions  of 
its  salts  by  reducing  agents  such  as  formic  acid. 

The  high  melting  point  of  platinum  (about  i7yo0C.),  its 
malleability  and  ductility,  and  its  resistance  to  the  action  of 
all  acids  render  it  of  very  great  use  in  chemistry  and  in  many 
industries  ;  its  scarcity  is  a  matter  for  regret. 

Antimony  is  a  metallic-looking  substance  of  specific 
gravity  67,  and  melts  at  40°  C.  It  is  very  brittle,  and  can 
easily  be  broken  and  ground  to  a  fine  powder.  It  shows  a 
strong  tendency  to  form  acidic  oxides.  Its  compounds  are 
poisonous. 

Bismuth  is  a  brittle  metal.  Its  colour  is  grey  with  a 
slightly  red  tinge.  The  basic  nitrate  is  used  in  medicine  as 
"  subnitrate  "  of  bismuth. 

Tin. — A  white  crystalline  metal  of  great  malleability.  Tin 
foil  is  largely  used  as  an  ornamental  and  air-tight  packing 
material.  Sometimes,  if  kept  at  a  low  temperature,  tin  slowly 
changes  into  a  grey  powdery  modification.  It  does  not 
oxidise  in  the  air,  and  is  therefore  employed  for  protecting 
iron,  plates  of  this  metal  being  dipped  into  molten  tin.  The 
tin-covered  iron  is  known  as  "  tin-plate,"  and  all  the  various 
forms  of  canisters,  commonly  known  as  "tins,"  are  made 


SOME   COMMON   METALS  213 

from   it.T     Copper  vessels  are  sometimes  coated  with  it,  as 
are  also  common  pins. 

Tin  is  attacked  by  hydrochloric  acid  ;  stannous  chloride, 
SnCl2,  is  formed  and  hydrogen  is  liberated.  Stannous  chloride 
is  known  commercially  as  tin  salt,  and  is  used  as  a  "  mordant  " 
in  dyeing.  The  action  of  chlorine  gas  upon  tin  leads  to  the 
formation  of  the  liquid  stannic  chloride,  SnCJ4.  The  metal  is 
also  attacked  by  nitric  acid,  the  cold  dilute  acid  giving 
stannous  nitrate  — 


4Sn  -f-  ioHNO,->4Sn(NO,),  +  3H2O  +  NH4NO, 

Concentrated  nitric  acid  yields  stannic  nitrate,  which  is, 
however,  at  the  temperature  of  the  reaction,  decomposed  by 
water,  yielding  metastannic  acid,  H10Sn5O15. 

5Sn  +  2oHNO3->  HjoSnAs  +  2oNO2  +  5H2O 

On  heating  the  white  solid  metastannic  acid,  a  straw-coloured 
powder  of  stannic  oxide,  SnO2,  is  left. 

Tin  forms  two  sulphides,  stannous  sulphide  (SnS),  which  is 
thrown  down  as  a  brown  precipitate  when  sulphuretted  hydro- 
gen is  passed  through  a  solution  'of  a  stannous  salt,  and  stannic 
sulphide,  SnS2,  can  be  obtained  as  a  yellow  precipitate  from 
stannic  salts  in  the  same  manner.  Stannic  sulphide  is  also 
made  by  heating  together  tin  filings,  sulphur,  ammonium 
chloride,  and  mercury  ;  the  ammonium  chloride  and  the  mer- 
cury are  volatilised,  and  stannic  sulphide  is  left  as  a  brilliant 
yellow  crystalline  solid.  It  is  used  in  jewellery  and  enamel 
work  as  "  Mosaic  gold,"  also  as  a  "  Bronze  powder." 

The  oxide,  SnO2,  is  used  in  pottery  for  the  preparation  of 
a  white  enamel. 

Arsenic.  —  The  element  arsenic  possesses  so  few  of  the 
metallic  properties,  that  it  is  generally  classed  among  the  non- 
metals.  It  is  closely  related  to  phosphorus  in  most  of  its 
chemical  properties.  In  its  most  common  form  it  is  a  dark 
grey  crystalline  substance  with  a  metallic  lustre.  At  ordinary 
pressure  it  does  not  melt,  but  on  being  heated  passes  at  once 

1  Tin  is  not  attacked  by  water,  and  iron  vessels  protected  with  this 
metal  can  therefore  be  safely  used  as  drinking-vessels,  or  for  holding  milk, 


2i4     A   FOUNDATION   COURSE    IN    CHEMISTRY 

into  a  brownish-yellow  vapour.  Various  allotropic  forms  are 
known. 

When  arsenic  is  heated  in  presence  of  oxygen  it  burns  with 
a  brilliant  white  flame,  forming  an  oxide,  As4O6,  This  is 
generally  referred  to  as  arsenic  trioxide  ;  its  formula  is  some- 
times given  as  As2O3,  but  the  density  of  the  vapour  is  198, 
which  corresponds  to  a  molecular  weight  of  396,  and  this 
agrees  with  the  formula  first  written. 

This  oxide  is  the  commonest  compound  of  arsenic,  and  is 
usually  known  as  "White  Arsenic."  It  is  an  acidic  oxide 
which  dissolves  in  alkalies  and  in  alkaline  carbonates,  forming 
arsenites  — 

i2NaOH  +  As4O6-»4Na3AsO3  +  6H2O 


When  manufactured  on  a  large  scale,  it  first  appears  as  a 
transparent  glassy  material  (amorphous),  which,  on  keeping, 
gradually  becomes  white  and  opaque  like  porcelain  (crystalline). 

All  the  compounds  of  arsenic  are  extremely  poisonous,  and 
many  of  them  are  characterised  by  an  objectionable  garlic-like 
odour. 

If  white  arsenic  be  treated  with  nitric  acid,  arsenic  acid, 
H3AsO4,  crystallises  out.  This  acid  is  in  many  respects 
similar  to  orthophosphoric  acid,  and  its  salts  yield  a  yellow 
precipitate  with  ammonium  molybdate.*  When  heated,  arsenic 
acid  loses  water  and  leaves  the  pentoxide,  which,  on  being 
more  strongly  heated,  decomposes  into  oxygen  and  As4O6. 

Arsenic  combines  with  hydrogen,  forming  the  hydride 
AsH3  (arsenietted  hydrogen),  an  extremely  poisonous  gas, 
which  is  produced  whenever  hydrogen  is  liberated  in  the 
presence  of  arsenic  or  its  compounds. 

The  liberation  of  the  gas  forms  a  very  delicate  test  for 
arsenic.  If,  for  instance,  hydrogen  be  liberated  from  zinc  and 
dilute  sulphuric  acid,  and  a  very  small  quantity  of  an  arsenic 
compound  placed  in  the  apparatus  with  the  mixture,  arsenietted 
hydrogen,  AsH3,  is  evolved  with  the  hydrogen,  and  if  the  gas 
is  passed  through  a  hard  glass  tube  heated  at  one  point,  the 

*  Ammonium  molybdate  also  gives  a  yellow  precipitate  with  phosphates 
in  nitric  acid  solution. 


SOME   COMMON    METALS  215 

presence  of  the  arsenic  is  shown  by  the  formation  of  a  black 
mirror-like  deposit.  This  deposit  is  arsenic  formed  by  the 
decomposition  of  the  hydride.  Antimony  hydride,  SbH3,  can 
be  prepared  in  a  similar  manner,  and  it  behaves  in  the  same 
way,  but  the  deposits  may  be  distinguished  by  the  solubility 
of  the  arsenic  mirror  in  sodium  hypochlorite.  A  more  simple 
way  of  showing  the  presence  of  arsenic  hydride,  and  therefore 
of  arsenic,  is  to  liberate  hydrogen  as  described  above,  adding 
the  substance  suspected  of  containing  arsenic,  and  to  burn  the 
gas  at  a  jet.  On  holding  a  piece  of  cold  porcelain  in  the 
flame  a  black  lustrous  deposit  of  arsenic  is  obtained. 

Arsenic  is  precipitated  from  its  solutions  by  sulphuretted 
hydrogen  as  a  yellow  sulphide,  As2S3,  soluble  in  solutions  of 
alkalis  or  of  alkaline  sulphides,  also  in  a  solution  of  ammonium 
carbonate. 


216     A    FOUNDATION    COURSE    IN    CHEMISTRY 


SOME  IMPORTANT  ALLOYS,  WITH  THEIR  APPROXIMATE  COMPOSITION. 


Per  cent. 

Aluminium  bronze     . 

Copper      .     90 

A  bright  gold-coloured  alloy, 

Aluminium     10 

hard  and  tenacious. 

Gun  metal    .... 

Copper      .     90 
Tin  .     .     .     10 

Reddish  -yellow    metal,    tough 
and    tenacious.       It    is   the 

material  of  which  large  guns 

were  formerly  cast. 

Bell  metal    .... 

Copper       .     78 

Yellowish-grey     alloy,     hard, 

Tin  .     .     .     22 

brittle,  and  very  sonorous. 

Brass  (many  varieties 

Copper      .     71-4 

This    is    the    composition    of 

of    this    alloy    are 

Zinc      .     .     28-6 

ordinary  brass.     It  is  a  pale 

made) 

yellow  alloy. 

Copper      .     60 

This   is    the    alloy  known   as 

Zinc      .     .     40 

Muntz  metal. 

Bronze     

Copper      .     88 

This  is  one  of  the  bronzes  used 

Tin  ...       9 

for  statuary.     Some  bronzes 

Zinc      .     .       2 

contain  copper  and  tin  only. 

Lead     .     .       I 

% 

German  silver  .     .     . 

Copper       .     50 
Nickel  .     .     26 

A  white  alloy.     A  good  imita- 
tion of  silver.    German  silver 

Zinc      .     .     24 

is  sometimes   made   without 

zinc. 

Pewter     

Tin  ...     90 

A    pale    grey   alloy   taking   a 

Antimony  .       7 

high  polish. 

Bismuth     .       2 

Copper       .       i 

Solder  (soft)      .     .     . 

Lead     .     .     33-3 
Tin  .         .    66-6 

Many  solders  are  made,  suit- 
{       able  for  various  purposes. 

Type  metal  .... 

Lead     .     .     80 

The  melted  alloy  expands  at 

Antimony  .     20 

the  moment  of  solidification. 

Shot  or  Bullet  metal  . 

Lead     .     .     98 

Arsenic      .       2 

SOME   COMMON    METALS 


217 


International  Atomic  Weights. 


0 

=  16. 

0 

=  16. 

Aluminium    . 

Al 

27-1 

Neodymium 

Nd 

I44-3 

Antimony      . 

.     .     Sb 

120*2 

Neon        . 

Ne 

20-2 

Argon 

.      .     A 

39-88 

Nickel     .... 

Ni 

58-68 

Arsenic    . 

.      .     As 

74-96 

Niton  (radium  ema- 

Barium   . 

.      .     Ba 

I37-3 

nation) 

Nta 

,222-4 

Bismuth  . 

.      .     Bi 

208-0 

Nitrogen       .     .      . 

N 

I4'OI 

Boron 

.      .     B 

II'O 

Osmium  .... 

Os 

190-9 

Bromine  . 

.      .     Br 

79*92 

Oxygen    .... 

O 

16-00 

Cadmium 

.      .     Cd 

112-40 

Palladium 

Pd 

106-7 

Caesium    . 

.      .     Cs 

132-81 

Phosphorus  .     .     . 

P 

31-04 

Calcium  . 

.      .     Ca 

40-07 

Platinum 

Pt 

195-2 

Carbon     .     . 

.      .     C 

12-00 

Potassium 

K 

39-10 

Cerium    ,      . 

.     .     Ce 

I40-25 

Praseodymium    . 

Pr 

140-6 

Chlorine  . 

.     .     Cl 

35'46 

Radium   .... 

Ra 

226-4 

Chromium     . 

.      .     Cr 

52-0 

Rhodium 

Rh 

102*9 

Cobalt     .      . 

.     Co 

58'97 

Rubidium 

Rb 

85-54 

Columbium  . 

.     Cb 

93'5 

Ruthenium    . 

Ru 

101-7 

Copper     .      . 

.      .     Cu 

63-57 

Samarium 

Sa 

I5°'4 

Dysprosium  . 
Erbium    . 

:  :  £ 

162-5 
1677 

Scandium 
Selenium 

Sc 
Se 

44-1 
79-2 

Europium 

.     .     Eu 

152-0 

Silicon     .... 

Si 

28*3 

Fluorine 

.     .     F 

19-0 

Silver       .... 

Ag 

107*88 

Gadolinium*  . 

.     .     Gd 

157-3 

Sodium    .... 

Na 

23-00 

Gallium   . 

.     .     Ga 

69-9 

Strontium 

Sr 

87-63 

Germanium   . 

.      .     Ge 

72'C 

Sulphur 

s 

32'O7 

Glucinum 

.     .     Gl 

/  •*  J 
9'I 

Tantalum 

Ta 

•j        i 

181-5 

Gold  .      .      . 

.     .     Au 

I97-2 

Tellurium 

Te 

127-5 

Helium    . 

.      .     He 

3  '99 

Terbium        .      .      . 

Tb 

159-2 

Holmium 

.     .     Ho 

!63"5 

Thallium        .      .      . 

Tl 

204*0 

Hydrogen 

.      .     II 

i  -008 

Thorium 

Th 

232*4 

Indium     . 

.      .     In 

114-8 

Thulium 

Tm 

168-5 

Iodine 

.      .     I 

126*92 

Tin     

Sn 

1  19-0 

Indium    . 

.      .      Ir 

193-1 

Titanium 

Ti 

-7 

48-1 

Iron 

.      .     Fe 

55-84 

Tungsten 

W 

184-0 

Krypton  . 

.      -     Kr 

82-92 

Uranium 

U 

238-5 

Lanthanum   . 

.      .     La 

139*0 

Vanadium 

V 

51-0 

Lead  . 

.      .     Pb 

207'  10 

Xenon      .... 

Xe 

130-2 

Lithium   . 

.      .     Li 

6-94 

Ytterbium     (Neoyt- 

Lutecium 

.      .     Lu 

174-0 

terbium)     . 

Yb 

172-0 

Magnesium  . 

.      .     Mg 

24-32 

Yttrium   .... 

Yt 

89-0 

Manganese    . 

.     Mn 

CA'Q'* 

Zinc         .            .      . 

Zn 

6C  "37 

Mercury 

.      .     Hg 

34  yj 
200-6 

Zirconium 

Zr 

->  O/ 
90*6 

Molybdenum 

.      .     Mo 

96-0 

APPENDIX 

WEIGHTS,   MEASURES,   ETC. 

Measures  of  Length. 

The  English  yard  is  the  distance  at  62°  F.  between  two  marks 
on  a  bronze  bar  deposited  at  the  offices  of  the  Board  of  Trade.1 

The  metre  is  the  length  at  o°  C.  of  a  platinum  bar,  preserved 
at  Paris.  It  was  intended  to  be  one  ten-millionth  part  of  the 
earth's  quadrant. 

i  yard  =  0*9144  m.  i  metre          =    1*0936  yard, 

i  foot   =  0*3048  m.  ,,  =    3-2809  feet, 

i  inch  =  0*0254  m.  „  =  39-37  inches, 

i  centimetre  =    0*3937  inch. 
*>.  nearly  *  inch, 
i  kilometre    =    0*6214  mile. 
/>.  nearly  g  mile. 
Pleasures  of  Capacity. 

English — i  pint      =  34*683  cub.  inches  =  568*23  c.  cm. 
i  gallon  =    0*1 6  cub.  foot  4*546  litres. 

Metric — i  litre      =    i  cubic  decimetre  =    61-0363  cub.  inches 

=    1*76  pint  =  0*2201  gallon. 
One  gallon  of  water  weighs  10  Ibs. 
One  cubic  foot  of  water  at  39°  F.  weighs  62*415  Ibs.,  i.e.  nearly 

IOOO  OZS. 

• 

Measures  of  Mass. 

English— i  pound  av.  =  7000  grains  =  453*593  grams, 

i  ounce  av.  =    437-5  grains  =    28*35  grains. 

Metric — i  gram          =  mass  of  i  c.  cm.  of  water  =    15*43  grains. 
i  kilogram  =  1000  grams  =      2*2046  Ibs. 

1  Copies  of  the  English  Standard  Yard  and  other  English  measures 
may  be  seen  on  the  steps  on  the  north  side  of  Trafalgar  Square,  London. 


APPENDIX  219 

Miscellaneous  Data. 

Mass  of  I  cub.  foot  of  air          =      ofo8o728  Ib. 
Mass  of  I  litre  of  air  =      1-2932  grams. 

Normal  atmospheric  pressure  =  760  mm.  of  mercury 

=    29-922  inches  of  mercury. 

A  halfpenny  is  one  inch  in  diameter  and  weighs          0*2  ounce. 
Latent  heat  of  water  ......    *    fc    ^;«        79'25 

Latent  heat  of  steam „  ,,   .   536 


QUESTIONS 

1.  What  do  you   understand    by  the    terms   "Matter"    and 
"  Energy  ".? 

2.  What  is  meant  by  (a)  "  Force,"  (J)  "  Mechanical  Work  "? 

3.  Distinguish    between    a    "physical"    and    a    "chemical" 
change. 

4.  What  is  the  effect  of  continued  heating  upon  sulphur,  ice, 
iodine,  oxide  of  mercury,  chalk  ?    Which  of  these  undergo  chemical 
change  when  heated  ? 

5.  Give  examples  of  chemical  change,  and  show  in  each  case 
how  you  would  know  that  a  chemical  change  had  occurred. 

6.  What  is  double  decomposition  ?    What  kinds  of  substances 
can  take  part  in  such  a  change,  and  under  what  conditions  ? 

7.  What  are  the  chief  points  of  difference  between  mixtures  and 
compounds  ? 

8.  Classify     the    following    as     elements,    compounds,    and 
mixtures  : — iron,   brass,  lime,   blue  vitriol,   common   salt,   sugar, 
sulphur,  mortar,  air,  charcoal,  sulphide  of  iron,  water,  red-lead. 

9.  Distinguish  between  the  terms  "  Mass  "  and  "  Weight." 

10.  Describe  carefully  what  you   observe  when   sulphur  and 
iron  filings  are  mixed  together  and  heated. 

11.  Classify  the  following  as  physical  and  chemical  changes  : — 
The  rusting  of  iron,  the  electrification  of  vulcanite,  the  slaking  of 
lime,  the  melting  of  ice,  the  magnetisation  of  steel,  decay,  the 
burning  of  coal,  the  making  of  a  photographic  print,  the  drying 
of  gum,  the  hardening  of  varnish,  and  the  drying  of  paint. 


220  APPENDIX 

12.  How  would   you  separate  each  of  the  following  mixtures 
into  its  components  ? — 

(1)  A  mixture  of  sulphur  and  iron  filings. 

(2)  „  „  sand  and  salt. 

(3)  „  .  „  charcoal  and  sugar. 

(4)  »  „  iodine  and  charcoal. 

(5)  ,,  „  sugar  and  salt. 

(6)  Black  gunpowder. 

13.  Mention  some   of  the   properties  by  virtue  of  which  the 
following  substances  have  commercial  value : — Iron,  copper,  coal, 
petroleum,  limestone,  platinum,  oxygen. 

14.  Explain  how  it  is  that  a  waterfall  may  have  commercial 
value. 

15.  State  Boyle's  Law.      How  can  it  be  proved  experimentally  ? 

1 6.  What  is  a  "  Natural  Law  "  ?     State  the  law  which  expresses 
the  relation  between  the  volume  of  a  gas  and  the  temperature  at 
which  it  exists.     Describe  experimental  proofs  of  this  law. 

17.  What    instrument    is  used    for    measuring    temperature? 
Describe  the  construction  of  a  usual  form  of  this  instrument. 

18.  What  is  a  degree  Centigrade?     Compare  the  values  of  the 
Centigrade,  Rdaumur,  and  Fahrenheit  degrees. 

19.  What  is  "Absolute  Temperature"?     Show  that  Charles' 
Law  may  be  expressed  in  the  form,  "The  volume  of  a  gas  is 
proportional  to  its  absolute  temperature." 

20.  How  would  you  prepare  and  collect  a  few  jars  of  oxygen  ? 
Describe  experiments  for  demonstrating  the  properties  of  the  gas. 

21.  What  do  you  understand  by  the  term  "  combustion  "?   What 
is  a  "  supporter  of  combustion  "  ? 

22.  In  what  respects  does  the  rusting  of  iron  differ  from  what 
takes  place  when  iron  is  burned  in  oxygen  ? 

23.  What  are  the  usual  methods  employed  in  the  commercial 
preparation  of  oxygen  ? 

24.  How  is  oxygen  obtained  from  potassium   chlorate?     By 
what  means  can  the  evolution  of  the  gas  be  facilitated  ? 

25.  What  happens  when  the  following  substances  are  strongly 
heated  in  contact  with  the  air : — Copper,  tin,  iron,  magnesium, 
potassium  chlorate,  gold,  sulphur,  phosphorus  ? 

26.  What  is  the  relation  of  the  oxygen  in  the  air  to  respiration? 

27.  How  could  you  obtain  nitrogen  from  air  ?    What  are  the 
chief  properties  of  the  gas  ?     How  can  it  be  made  to  combine  with 
(a)  oxygen,  (V)  magnesium  ? 

28.  Compare  the  effects  of  burning  the  following  in  an  enclosed 
volume  of  air  : — Phosphorus,  a  candle,  coal  gas. 


APPENDIX  221 

29.  Describe  an  experiment  which  shows  that  the  boiling  point 
of  a  liquid  is  dependent  upon  the  pressure. 

30.  Account  for  the  fact  that  water  is  never  found  in  nature 
in  a  pure  state.     Mention  some  of  the  more  common  impurities. 

31.  Describe  the  effect  upon  the  volume  of  water  by  cooling  it 
from  15°  C.  to  -  15°  C. 

32.  What  are  the  advantages  of  the  use  of  hot  water  or  steam 
for  warming  buildings  ? 

33.  Impurities   in  water  may  be   either  in   suspension   or  in 
solution.     Distinguish  between  these  two  conditions. 

34.  Describe  a  solubility  curve.     Construct  one  for  ammonium 
chloride  from  the  following  figures. 


Temperature  in  ^f"!" JFJ"18  Temperature  in  Mass  in  grams 

degreefcentigrade.      ,„*%£*&*,.    degree,"  Centigrade.      Jg**,*^. 

-15°  24-5  grams.  50°  50-4  grams. 


60°  55-2  „ 

5°  3i'2      „  70°  602  „ 

15°  35'2      „  80°  65-6  „ 

20°  37-2      „  90°  71-3  „ 

30°  4i'4      »  100°  77 '3      „ 

4o°  45*8      „  uo°  83-8      „ 

35.  Compare   the   solubility   of    solids    and    gases    in   water, 
particularly  as  regards  the  influence  of  temperature  and  pressure 
upon  the  amount  dissolved. 

36.  What    is   a  crystal?     How    could    you    obtain    (a)   lead 
chloride,  (I)}  common  salt,  in  a  crystalline  form  ? 

37.  Explain    the    term     "  Water    of    crystallisation."       Give 
examples  of  substances  which  contain  it. 

38.  What  information  would  you  require  before  you  permitted 
any  particular  water  to  be  used  for  drinking  purposes  ? 

39.  How  would  you  carry  out  the  electrolysis  of  water  ?     Make 
a  sketch  of  the  necessary  apparatus.     What  information  does  the 
electrolysis  give  you  as  to  the  composition  of  water  ? 

40.  By   what   methods    is   hydrogen   obtainable  from   water  ? 
What  is  the  action  of  metallic  sodium  upon  water  ?     Compare  it 
with  that  of  potassium  and  of  calcium  respectively. 

41.  How  could  hydrogen  be  obtained  from  sulphuric  acid? 

42.  Describe  experiments  illustrating   the  chief  properties   of 
hydrogen. 

43.  Hydrogen  is  said  to  be  a  reducing  agent.     How  would  you 
demonstrate  this  by  experiment  ? 


222  APPENDIX 

44.  Show   how  the   reduction  of  copper   oxide   by   hydrogen 
provides   a  means  of  determining  the  composition  of  water  by 
weight. 

45.  How  would  you  show  that  water  is  one  of  the  products  of 
combustion  of  a  candle  ? 

46.  Why  are  the  common  names  of  familiar  substances  not  in 
general  use  in  chemistry  ? 

47.  Distinguish  between  a  symbol,  a  formula,  and  an  equation. 
Classify  the  following :— Ca,  CaCl2,  Cu,  Co,  CO,  O,  O2,  O3,  H2O. 
Why  are  the  symbols  Na  and  Fe  respectively  used  for  sodium  and 
iron? 

48.  Why  do  we  speak  of  the  laws  of  definite  and   multiple 
proportions,  and  of  the  atomic  theory  f 

49.  What  is  the  difference  between  the  atomic  and  molecular 
weight  of  an  element  ?    Would  it  be  wrong  to  apply  either  of  these 
terms  to  compounds  ?  if  so,  why  ? 

50.  Show  that  the  '*  equivalent  "  of  some  elements  is  the  same 
as  the  atomic  weight,  and  in  other  cases  it  is  only  a  fraction  of  the 
atomic  weight.     How  do  you  account  for  this  ? 

51.  What  do  you  understand  by  the  term  "percentage  com- 
position "   of   a  substance  ?      Show   how   to   calculate  from  the 
formula  (a)  the  percentage  composition  of  a  compound,  (b}  the 
amount  by  weight  of  each  component  in  any  other  stated  quantity. 

52.  What  is  the  meaning  of  the   signs,   +  ,  — >,  v=^,  used  in 
writing  equations  ? 

53.  Explain  fully  the  meaning  of  the  equation — 

Zn  +  H2SO4->  ZnSO4  +  H2. 
Correct  the  following" equations  : — 

(1)  CaC03  +  HCl->CaCl2  +  H2O  +  CO2. 

(2)  Zn  +  2H2SO4->  ZnSO4  +  2H2O. 

54.  Compare   the  following  formulae   and  show  what   is   the 
valency  of  each  of  the  elements  represented  : — 

X) 

0  =  Mn  =  0  Ba<   | 

X0 

55.  Write    down     constitutional    formulas    for    each    of    the 
following  : — Magnesium  pyrophosphate,  dichlor-ethane,  ethylene- 
dichloride,   ethylene,  acetylene,  hydrocyanic   acid,   grape  sugar, 
soap,  fat,  benzene. 

56.  Distinguish  between  an  acidic  and  a  basic  oxide. 

57.  What  are  the  chief  properties  of  (a)  acids,  (£)  alkalis. 


APPENDIX  223 

58.  What  are   salts  ?      Mention  various  ways  in  which   they 
may  be  prepared. 

59.  Why  are  the  acids  often  referred  to  as  salts  of  hydrogen  ? 

60.  What  is  the  action  of  (a)  dilute  sulphuric  acid,  (ff)  hydro- 
chloric acid,  upon  the  following  metals  : — Iron,  zinc,  magnesium, 
copper,  aluminium  ?  Write  equations  representing  these  reactions. 

61.  Give  examples  of  a  mono-basic,  a  di-basic,  and  a  tri-basic 
acid,  and  write  the  formulae  of  the  normal  salts  which  each  forms 
with  potassium,  calcium,  and  aluminium. 

62.  How  would  you  show  that  sulphuric  acid  is  di-basic  ? 

63.  Normal   sodium   sulphate  yields   a  neutral   solution  with 
water,  while  a  solution  of  normal  sodium  phosphate  (Na3PO4)  is 
alkaline.     How  do  you  account  for  the  difference  ? 

64.  What  is  the  action  of  heat  upon  the  following  oxides : — 
Copper  oxide  (CuO),  lime,  litharge,  lead  dioxide,  manganese  dioxide, 
barium  peroxide,  mercuric  oxide,  zinc  oxide  ? 

65.  Compare  the  action  of  hydrochloric  acid  upon  the  peroxides 
of  manganese  and  barium. 

66.  What  can  be  observed  when  a  solution  of  hydrogen  per- 
oxide   is    allowed    to    act    upon  (a)   an   acidulated    solution    of 
potassium  iodide,  and  (£)  a  solution  of  potassium  permanganate 
acidulated  with  sulphuric  acid  ? 

67.  In  what  forms  does  calcium  occur  in  nature  ? 

68.  Describe   the  industrial   process  known   as   lime-burning. 
Criticise  the  term. 

69.  What  is  a  reversible  reaction  ?    Why  is  the  action  between 
lime  and  carbon  dioxide  considered  reversible  ? 

70.  What  is  mortar?     Discuss  the  changes  which  take  place 
when  it  hardens. 

71.  What  is  gypsum?     What  changes  take  place  in  it  when 
it  is  heated  ? 

'    72.  What  is  the  cause  of  the  "  setting  "  of  plaster  of  Paris  ? 

73.  What  compounds  are  formed  when  carbon  dioxide  is  passed 
for  a  long  time  into  (a)  caustic  soda,  (b)  barium  hydroxide,  (^lime- 
water  ? 

74.  What  are  the  various  causes  of  "  hardness  "  in  water  ? 

75.  What  is  boiler  "fur"  or  "scale"?     How  is  it  produced, 
and  in  what  way  may  its  formation  be  prevented  ? 

76.  What  are  the  chief  processes  used   for  softening   water 
intended  for  drinking  ? 

77.  How  is   the  liquefaction  of  gases  generally  carried   out? 
What  do  you  understand  by  the  terms  "  critical  temperature  "  and 
"  critical  pressure  "  ? 


224  APPENDIX 

78.  How    would    you    show    that    carbon    dioxide    contains 
carbon  ? 

79.  Why  do  we  represent  carbon  dioxide  by  the  formula  CO2, 
and  carbon  monoxide  by  the  formula  CO  ? 

80.  Discuss  the  various  causes  of  "  stuffiness  "  in  rooms. 

81.  What  is  a  carbonate?     What  is  the  general  action  of  acids 
upon  carbonates  ?    Give  examples  with  equations. 

82.  Discuss  the  relation  of  carbon  dioxide  to  plant  and  animal 
life. 

83.  Give  an  account  of  the  natural  occurrence,  properties  and 
uses  of  common  salt. 

84.  How  would  you  prepare  and  collect   a  few  jars  of  dry 
hydrochloric  acid  gas  ? 

85.  Account  for  the  name  oxy-muriatic  acid  which  was  originally 
given  to  the  gas  now  known  as  chlorine. 

86.  What  is  the  effect  of  treating  hydrochloric  acid  with  oxidising 
agents  ?     Write  equations  representing  the  interaction  of  the  acid 
with  manganese   dioxide,  potassium  bichromate,  potassium  per- 
manganate.   What  are  the  chief  properties  of  the  gas  evolved  ? 

87.  Four  jars  of  gas  are  given  to  you^ 

(a)  contains  carbon  dioxide 

(b)  „        nitrogen 

(c)  „        hydrogen 

(d)  „        chlorine. 

By  what  tests  could  you  identify  the  contents  of  each  jar  ? 

88.  State  Avogadro's  hypothesis,  and  show  how  it  enables  us 
to  compare  the  weights  of  the  molecules  of  gases. 

89.  Why  is  hydrochloric  acid  gas  represented  by  the  formula 
HC1? 

90.  What  is  aqua    regia?      Explain  why  its  properties  differ 
from  those  of  either  of  the  acids  of  which  it  is  composed. 

91.  What  methods  are  in   use  for  the  preparation  of  soda'- 
crystals  ? 

92.  Write  chemical  formulae  for   the  following  common  sub- 
stances : — Caustic  soda,  washing   soda,  common   salt,  limestone, 
quicklime,  Glauber  salt,  Chili  saltpetre,  borax.     What  is  the  effect 
of  heat  upon  these  substances  ? 

93.  In  what  forms  does  sulphur  occur  in  nature  ?     How  is  it 
obtained  in  a  pure  state  ? 

94.  Sulphur  is  said  to   exhibit  allotropy.     Explain  the  term, 
and  show  how  the  various  allotropic  modifications  of  sulphur  may 
be  obtained. 

95.  What  is  the  action  of  hydrochloric  acid  upon  (a)  iron,  (d) 


APPENDIX  225 

sulphur,  (c)  a  mixture  of  iron  and  sulphur,  (d)  the  substance  formed 
when  iron  and  sulphur  are  heated  together  ? 

96.  Complete  the  following  equations  : — 

C  +  2H2S04  -» 

S  +  2H2SO4  -> 
Cu  +  2H2SO,  -» 
Zn  +  H2SO4  -> 

What  are  the  conditions  under  which  the  reactions  represented  by 
these  equations  most  readily  take  place  ? 

97.  Give  a  short  account  of  the  method  generally  employed  for 
preparing  sulphuric  acid  on  a  commercial  scale. 

98.  Comment  upon  the  following  names,  all  of  which  are  applied 
to  a  solution  of  the  same  gas  in  water :— Sulphuretted  hydrogen, 
hydrogen  sulphide,  hydrosulphuric  acid. 

99.  What  is  ozone?     How  can  it  be  prepared?     How  has  its 
constitution  been  discovered  ? 

100.  Compare  the  properties  of  ozone  with  those  of  oxygen  and 
hydrogen  peroxide. 

10 1.  What  difference,  if  any,  would  you  expect  to  find  in  the 
composition  of  wood  ashes,  coal  ashes,  and  bone  ashes  ? 

102.  What  are  now  the  chief  sources  of  potassium  compounds  ? 
How  can  the  metal  itself  be  obtained  from  its  chloride? 

103.  How  would  you  obtain  (a)  potassium  sulphate  from  potas- 
sium carbonate,   and   (b)    potassium  carbonate  from    potassium 
sulphate  ? 

104.  What  are  the  chief  points  of  difference  between  the  pro- 
perties of  the  yellow  and  red  modifications  of  phosphorus  ? 

105.  Describe  briefly  the  methods  employed  in  the  manufacture 
of  phosphorus,  and  show  what  is  the  special  function  of  each  of 
the  substances  used. 

106.  What  are  the.  essential  characteristics  of  sand  and  clay 
respectively?    Upon  what  do   these  properties  chiefly  depend? 
What  minerals  are  generally  present  in  each? 

107.  What  substances  enter  into  the  composition  of  ordinary 
glass  ? 

108.  What  is  the  chemical  composition  of  the  substances  com- 
mercially known    as  corundum,  superphosphate,   fluorspar,   car- 
borundum,  borax  ?      For  what    purposes   are    these    substances 
used  ? 

109.  Discuss  the  use  of  preservatives  in  food 

1 10.  What  are  the  chemical  actions  involved  in  the  various 

Q 


226  APPENDIX 

processes  of  bleaching?    What  substances  are  usually  employed 
for  this  purpose  ? 

in.  How  would  you  detect  boracic  acid  in  butter? 

112.  When  glass  is  brought  into  contact  with  hydrofluoric  acid, 
it  is  corroded.      What   chemical  actions  take   place,    and   what 
substances  are  formed  ? 

113.  Distinguish  between  colloid  and  crystalloid  substances. 
How  can  they  be  separated  from  each  other  when  in  solution  ? 

114.  What  is  meant  by  destructive  distillation?    Classify  the 
principal  products  obtained  by  destructive  distillation  of  wood  and 
coal  respectively. 

115.  What  is  water-gas?     How  is  it  made  and  for  what  is 
it  used? 

1 1 6.  What    are    the    experimental    reasons    for    representing 
ammonia  by  the  formula  NHS. 

1 17.  The  compound  NH4OH  (ammonium  hydroxide)  has  never 
been  isolated,  but  it  is  believed  that  it  exists  in  aqueous  solutions 
of  ammonia  gas.     Upon  what  experimental  evidence  is  this  belief 
based  ? 

1 1 8.  What  are  the  more  important  chemical  properties  of  nitric 
acid  ?    How  are  the  lower  oxides  of  nitrogen  obtained  from  it  ? 

119.  How  is  nitric  acid  prepared?    What  are  the  chief  com- 
mercial sources  of  the  acid  ? 

120.  State  precisely  what  would  be  observed  when  the  follow- 
ing  substances   are  heated   strongly  :— Ammonium  nitrate,  am- 
monium   chloride,   potassium    nitrate,   lead    nitrate,    ammonium 
carbonate,  silver  nitrate.     Express  the  reactions  which  take  place 
by  means  of  equations. 

121.  What  do  you  understand  by  the  term  "organic  matter"? 
What  are  the  elements  most  frequently  present  in  organic  matter  ? 

122.  What  is  the  object  of  filtering  water  through  charcoal? 
How  far  is  this  object  effected  ? 

123.  In  what  way  do  the  following  substances  differ  from  one 
another : — Peat,  lignite,  house  coal,  anthracite  ? 

124.  Name  some  of  the  most  important   by-products  of  the 
preparation  and  purification  of  coal-gas.     For  what  purposes  are 
they  employed  ? 

125.  What  are  the  chief  properties  of  the  gas  prepared  by  the 
action    of   concentrated    sulphuric    acid    upon    potassium   ferro- 
cyanide  ?    By  what  other  methods  can  the  gas  be  obtained  ? 

126.  What  is  sal-ammoniac?     From  what  did  it  receive  its 
name?    What  happens  when  it  is  heated  with  chalk? 

127.  What  is  an  ammonium  salt? 


APPENDIX  227 

128.  What  methods  are  now  employed  for  obtaining  the  nitrogen 
of  the  atmosphere  in  a  form  in  which  it  can  be  used  as  plant 
food? 

129.  Compare  the  forms  in  which  plants  and  animals  require 
nitrogenous  food. 

130.  What  is  the  nature  of  the  change  which  takes  place  when 
certain  carbohydrates  are  boiled  for  some  time  with  dilute  acid? 
What  substances  are  formed  when  cane  sugar,  starch,  milk  sugar, 
and  cellulose  respectively  are  treated  in  this  way  ? 

131.  What  is  an  enzyme?    Give  a  short  account  of  some  of 
the  changes  brought  about  by  their  action. 

132.  What  substances  are  formed  when  (a)  cane  sugar,  (£) 
metallic  copper  are  treated  with  concentrated  nitric  acid  ?    Men- 
tion the  chief  properties  of  the  solid  products. 

133.  How  would  you  show  the   presence  of  nitrogen   in   an 
organic  compound  ?     Upon  what  chemical  actions  is  your  method 
based  ? 

134.  What  is  the  action  of  heat  upon  the  following :— Cream  of 
tartar,  mercuric  cyanide,  ammonium  cyanate  ? 

135.  By  what  tests  would  you  recognise  cane  sugar,  glucose, 
and  starch  ? 

136.  What   connection   can    be    traced    between   marsh    gas, 
paraffin  oil,  and  vaseline?     Mention  any  other  commercial  pro- 
ducts of  similar  nature. 

137.  What  is  a- homologous    series?     Mention    homologous 
series  the    members   of  which  contain  (a)  oxygen,  (F)  chlorine, 
(c)  nitrogen,  (d)  none  of  these  elements.      Give  the  names  and 
formulae  of  substances  which  are  typical  members  of  each  of  the 
series  you  have  referred  to. 

138.  Why   is   common   alcohol    represented    by  the  formula 
C2H6OH  ?    By  what  other  names  is  the  substance  known  ?     How 
is  it  obtained  commercially?    Give  the  names  and  formulae  for 
any  six  other  alcohols,  and  show  how  these  formulas  represent 
their  common  properties  and  their  differences. 

139.  Describe  briefly  the  more  important  properties  of  alde- 
hydes.   What  relation  do  these  compounds  bear  (a)  to  alcohol, 
(<£)  to  acids  ?     How  would  you  experimentally  demonstrate  this 
relation  ? 

140.  Distinguish  between  an  ether  and  an  ester.     Describe  the 
method  of  preparation  of  one  of  each  of  these  compounds. 

141.  What  two  substances  can  be  represented  by  the  empirical 
formula  C2H6O  ?     How  would  you  distinguish  one  of  these  com- 
pounds from  the  other  ? 


228  APPENDIX 

142.  What  is  an  olefine?    Why  are  the  defines  regarded  as 
unsaturated  ?     How  is  this  condition  indicated  in  their  chemical 
formulae  ?     Write  the  general  formula  for  the  group. 

143.  Show  by  means  of  a  sketch  the  structure  of  an  ordinary 
candle  flame.    Why  do  the  flames  of  burning  alcohol,  hydrogen, 
and  a  Bunsen  burner  give  out  little  or  no  light  ? 

144.  What  is  the  difference  between  a  tertiary  alcohol  and  a 
tri-hydric  alcohol  ?     Give  examples  of  each. 

145.  What  is  the  difference    between  glycol  and  glycocol  ? 
What  products  are  obtained  by  the  oxidation  of  each  ? 

146.  How  is  soap  made  ?     Give  equations.     What  are  the 
characteristics  of  potash  soaps,  soda  soaps,  stearin  soaps,  olein 
soaps,  calcium  soaps,  ammonia  soaps,  lead  soaps  ?    What  is  the 
composition  of  ordinary  household  soap  ? 

147.  Distinguish   between   a   "carbohydrate"   and   a   hydro- 
carbon. 

148.  Glucose  and  fructose  are  both  represented  by  the  empirical 
formula  C6H12O6,  yet  they  have  different  properties.     What  are 
these  differences,  how  are  they  accounted  for  ? 

149.  What  is  milk  sugar?     How  could  you  distinguish,  in  the 
laboratory,  between  cane  sugar  and  milk  sugar  ? 

150.  Explain  the  term  "hydrolysis."     By  what  agencies  are 
hydrolytic  changes  brought  about  ? 

151.  What  do  you  understand  by  fermentation  ?    Mention  four 
different  types  of  fermentation  and  give  the  name  of  the  chief 
product  in  each  case. 

152.  What   are  the  respective  actions  of  yeast  and   baking 
powder  in  dough  ?    Ammonium  carbonate  is  sometimes  used  as 
baking  powder  ;  what  is  its  action  ? 

153.  What  is  an  amine  ?    How  does  it  differ  from  an  amide  ? 

154.  What  are  "formalin  "  and  formamide  respectively  ? 

155.  What    is   the  chief  nitrogenous  compound   excreted  by 
animals  ?    Give  two  distinct  methods  by  which  it  may  be  artificially 
prepared. 

156.  What  do  you  know  of  the  following  naturally  occurring 
compounds  : — Amygdalin,  salicin,  citric  acid,  malic   acid,  starch, 
asparagin  ? 

157.  What    do   you    understand  by  the  terms,  "isomerism," 
"  polymerism  "  ?    Give  examples. 

1 58.  What  is  meant  by  the  "  flash  point "  of  a  lamp  oil  ?     What 
is  the  legal  flash  point  in  Great  Britain  ? 

159.  Mention  various  substances  which  are  in  common  use  as 
lubricants.     What  are  the  essential  properties  of  lubricants  ? 


APPENDIX 


229 


1 60.  What  is  a  fuel  ?     Compare  light  petroleum  and  alcohol  as 
fuels. 

161.  The  compounds,  marsh  gas,  ethylene,  and  acetylene  are 
respectively  represented  by  the  formulas— 

CH.,  CH 

CH,  |!    '  HI 

CH2  CH 

What  are  the  experimental  data  for  these  formulae  ? 

162.  Distinguish   between    a  "wax"  and   a  "fat."       What  is 
paraffin  wax  ? 

163.  By  what  tests  would  you  distinguish  between  a  mineral 
oil,  and  one  of  animal  or  vegetable  origin  ? 

164.  Contrast  the  action  of  concentrated  sulphuric  acid  upon 
a  paraffin  hydrocarbon  and  upon  benzene. 

165.  Write  a  short  account  of  the  substances  which  can  be 
formed  by  the  action  of  sulphuric  acid  upon  alcohol.    What  are 
the  conditions  most  favourable  to  the  formation  of  each  ? 

1 66.  In  what  respects  do  the  alcohols  resemble  the  hydroxides 
of  metals  ? 

167.  Account  for  the  cleansing  effect  of  soap.     What  is  the 
action  of  the  various  kinds  of  hard  water  upon  soap  ? 

168.  What  is  calcium  cyanamide  ?     Why  can  this  substance  be 
used  as  a  nitrogenous  manure  ? 

169.  What  is  coal  tar?    Account  for  its'commercial  importance. 

170.  What  is  benzene?     How  does  it  differ  from  the  liquid 
often  sold  as  benzine  ? 

171.  How  is  phenol  prepared?    What  are  its  chief  properties 
and  uses  ? 

172.  How  can  aniline  be  prepared  from  benzene?     Compare 
its  properties  with  those  of  ammonia. 

173.  Write  formulae  for  the  substances  commercially  known  as 
(i)  oil  of  mirbane,  (2)  oil  of  bitter   almonds,  (3)  carbolic   acid, 
(4)  oil  of  winter  green. 

174.  Criticise  the  name  "  carbolic  acid"  as  applied  to  phenol. 
Distinguish  between  a  phenol  and  an  alcohol. 

175.  What  is  a  "metal"  ?     Classify  the  following  as  metals  and 
non-metals: — Silver,  arsenic,   phosphorus,  potassium,   gold,   alu- 
minium, sulphur,  hydrogen,  silicon,  magnesium.     Give  reasons  for 
your  classification. 

176.  What  is  dolomite?     How  would  you  prepare  from  it  some 
crystallised  magnesium  sulphate  ? 

177.  Discuss  the  suitability  of  aluminium  for  cooking  utensils. 


230  APPENDIX 

178.  What  use  is  made  of  aluminium  compounds  in  dyeing? 
What  other  compounds  are  used  for  a  similar  purpose  ? 

179.  What  are  the  chemical  actions  involved  in  iron  smelting? 

1 80.  Distinguish  between  wrought  iron,  cast  iron,  and  steel. 

181.  What  is  basic  slag  ?     For  what  purposes  is  it  used  ? 

182.  What  happens  when  steam  is  passed  over  red-hot  iron, 
and  when  hydrogen  is  passed  over  red-hot  iron  oxide  ?     Explain 
why  these  reactions  take  place. 

183.  When  lead  oxide  is  warmed  with  a  slight  excess  of  dilute 
nitric  acid  it  dissolves.    What  is  produced,  and  how  can  it  be 
obtained  in  crystals  ?    What  would  you  observe  if  these  crystals 
were  heated  in  a  hard  glass  tube  ?    Give  equations  representing 
the  changes. 

184.  The   names  "Vitriol  of   Mars,"  green  vitriol,  copperas, 
sulphate  of  the  protoxide  of  iron,  ferrous  sulphate,  have  all  been  in 
use  at  some  time  or  other  for  the  same  compound.     Show  how 
they  indicate  the  progress  of  chemical  knowledge. 

185.  Distinguish  between  a  ferrous  and  a  ferric  salt.     How  can 
a  ferrous  be  converted  into  a  ferric  salt,  and  a  ferric  into  a  ferrous 
salt? 

1 86.  The  following  commercial   materials   are  all   iron   com- 
pounds.    Write  their  formulae,  describe  them,  and  mention  their 
chief  uses.     Green  vitriol,  Prussian  blue,  Venetian  red,  jeweller's 
rouge. 

187.  What  are  the  most  familiar  compounds  of  manganese  ? 
In  what  ways  do  they  find  industrial  application  ? 

1 88.  Iron  is  often  covered  with  a  protective  coating  of  zinc, 
nickel,  or  tin.     How  are  these  coatings  put  on  the  iron  ? 

189.  What  substances  are  used  to  impart  a  violet,  blue,  yellow, 
green,  or  red  colour  to  glass  or  porcelain  ? 

190.  What  is  the  "  passive  state  "  ?   How  can  iron  and  chromium 
be  made  to  assume  this  state  ? 

191.  A  dilute  solution  of  cobalt  chloride  has  been  used  as  a 
writing  ink,  the  words  becoming  visible  only  on  warming.     What 
property  of  the  salt  is  thus  made  use  of?     Mention  any  parallel 
cases. 

192.  From  what  property  has  the  metal  chromium  received  its 
name?     Illustrate  your  answer  by  reference  to  the  compounds  of 
chromium. 

193.  What  are  the  chief  compounds  used  as  white  and  yellow 
pigments  ?    What  are  the  advantages  and  disadvantages  attending 
the  use  of  each  of  them  ? 

194.  Write  the  chemical  formulae  for  the  following  common 


APPENDIX  231 

ores  : — Zinc  blende,  iron  pyrites,  galena,  malachite,  cuprite,  copper 
pyrites,  pyrolusite,  bauxite,  cassiterite,  haematite. 

195.  If  you  were  given  some  black  copper  oxide,  how  would 
you  obtain  from  it  some  crystallised  copper  nitrate  ? 

196.  Compare  the  action  of  a  solution  of  caustic  soda  with  that 
of  ammonia  solution,  upon  a  solution  of  copper  sulphate. 

197.  State  carefully  what  changes  take  place  when  the  following 
chain  of  reactions  is  carried  out.     Give  equations. 

(1)  Copper  is  dissolved  in  concentrated  nitric  acid. 

(2)  The  solution   is  evaporated   with   concentrated   sulphuric 

acid. 

(3)  The  residue  is  dissolved  in  water. 

(4)  Zinc  turnings  are  placed  in  the  solution. 

198.  How  would  you   prepare  (i)  cuprous  oxide,  (2)  cuprous 
chloride,  (3)  cuprous  iodide  from  cupric  sulphate  ? 

199.  What  is  verdigris?    Account  for  the  green  colour  assumed 
by  a  copper  roof  which  has  been  exposed  for  a  long  time  to  the 
weather. 

200.  What  are  the  advantages   and  disadvantages   attending 
the  use  of  copper  for  cooking  utensils  ? 

201.  What  dangers  attend  the  use  of  lead  pipes  for  the  supply 
of  drinking  water?     With  what  kinds  of  natural  waters  is   the 
danger  greatest  ?    Why  ? 

202.  Compare  the  properties  of  the  oxides  of  lead  which  are 
represented  by  the  formulae  PbO,  Pb3O4,  PbO2. 

203.  Describe  the  substances  known   as   corrosive  sublimate 
and  calomel.     How  could  you  obtain  the  latter  from  the  former 
compound  ? 

204.  Account  for  the  blackening  of  silver  which  has  come  in 
contact  with  white  of  egg  or  with  vulcanised  indiarubber. 

205.  What  property  of  silver  salts  enables  them  to  be  used  in 
photography  ? 

206.  What  are  the  chief  uses  of  gold  other  than  for  jewellery 
and  coinage  ? 

207.  What    is    the   action   of    aqua    regia     upon    gold    and 
platinum?      What  is   the  effect   of  heat  upon    the    compounds 
formed  ? 

208.  What  are  solders  ?     For  what  purposes  are  they  used  ? 

209.  How  can  the  two  chlorides  of  tin  be  prepared  ? 

210.  Why    is     arsenic     generally    considered    a    non-metal? 
Compare  its  properties  with  those  of  antimony  and  phosphorus. 

211.  How  can  small  quantities  of  arsenic  be  detected  ? 

212.  Classify  the  following  as  acidic  and  basic  oxides.     What 


232  APPENDIX 

is  the  action  of  hydrochloric  acid  and  of  nitric  acid  and  caustic 
soda  upon  each.  Chromium  trioxide  CrO3,  arsenious  oxide  As4O6, 
cuprous  oxide  CuO,  zinc  oxide  ZnO,  alumina  A12O3,  litharge  PbO, 
chromic  oxide  Cr2O3,  tin  dioxide  SnO2. 


EXAMPLES   FOR   CALCULATION 

1.  Calculate  the  equivalent  of  magnesium  if  10  grams  of  the 
metal  combine  with  oxygen  to  form  16*67.  grams  of  the  oxide. 

2.  If  1-5  grams  of  zinc  are  dissolved  in  acid,  and  511   c.c.  of 
hydrogen  at  N.T.P.  are  liberated,  what  is  the  equivalent  of  zinc  ? 

3.  Calculate  the  percentage    composition    of   (i)    potassium 
permanganate    KMnO4,    (2)  cane  sugar  C12H22On,    (3)  ferrous 
sulphate  FeSO47H2O,  (4)  sodium  chlorate  NaClO3. 

4.  Calculate  the  formulae  of  the  four  compounds  whose  per- 
centage compositions  obtained  by  analysis  are  as  follows : — 


(i)  Carbon 
Hydrogen 
Nitrogen 
Oxygen 

(3)  Potassium 
Sulphur 
Oxygen 

5854 
4-07 
11-38 
26*01 

3071 
25-19 
44-09 

(2)  Sodium 
Sulphur 
Oxygen 
Water 

(4)  Potassium 
Iron 
Carbon 
Nitrogen 

14-29 

9'94 
19-87 
55-90 

42'39 
15-22 
19-56 
22-82 

5.  A  volume  of  500  cubic  centimetres  of  air  measured  at  N.T.P. 
has  its  pressure  increased  to  780  mm.,  and  its  temperature  raised 
to  15°  C.     What  volume  will  it  now  occupy  ? 

6.  A  volume  of  350  c.c.  of  gas  measured  at  N.T.P.  has  its 
pressure  raised  to  790  mm.     To  what  must  the  temperature  be 
increased  that  the  volume  may  remain  unaltered  ? 

7.  A  volume  of  gas  is  measured  at  770  mm.  and  I5°C.    The 
pressure  is  increased,  and  by  raising  the  temperature  to  63°  C.  the 
volume  is  kept  constant.   What  has  been  the  increase  in  pressure  ? 

8.  A  volume  of  gas  measured  at  normal  pressure  and  15°  C.  has 
its  temperature  raised  to  50°  C.     To  what  pressure  must  the  gas 
be  subjected  that  its  volume  may  be  one-half  of  the  original  volume  ? 

9.  What  volurne  of  chlorine  would  be  obtained  if  ig  grams  of 


APPENDIX  233 

manganese  dioxide  were  treated  with  hydrochloric  acid  ?    The  gas 
is  to  be  measured  at  N.T.P. 

10.  If  25  grams  of  calcium  carbonate  were  treated  with  hydro- 
chloric acid,  and  the  resulting  gas  passed  into  an  excess  of  caustic 
soda   solution,   what  would    be   the   increase  in  weight  of  this 
solution  ? 

11.  Five  grams  of  a  mixture  of  calcium  carbonate  and  an 
inactive  substance  were  treated  with  hydrochloric  acid  and  found 
to  lose  i '2  grams  in  weight.     Calculate  the  percentage  of  calcium 
carbonate  in  the  mixture. 

12.  What  weight  of  quicklime  is  obtainable  from  150  grams  of 
pure  calcium  carbonate  ? 

13.  If  5  grams  of  caustic  potash,  KOH,  be  neutralised  with  sul- 
phuric acid,  what  weight  of  potassium  sulphate  would  be  obtained  ? 

14.  What  weight  of  copper  oxide,  CuO,  would  be  required  to 
combine  with  200  grams  of  a  solution  of  sulphuric  acid  containing 
49  per  cent,  of  pure  acid  (H2SO4)  ?    What  weight  of  crystallised 
copper  sulphate  would  be  formed  ? 

15.  If  3  litres  of  a  mixture  of  oxygen  and  ozone  (measured  at  a 
temperature  of  15°  C.),  containing   5  per  cent,  of  the  latter,  be 
heated  to  250°  C.,  what  will  be  the  volume  of  the  gas  at  this  latter 
temperature,  pressure  remaining  constant  ? 

1 6.  What  volume  of  sulphuretted  hydrogen  at  N.T.P.   could 
be  obtained  by  the  action  upon  ferrous  sulphide  of  15  grams  of  a 
solution  of  hydrochloric  acid  containing  40  per  cent,  of  the  gas 
(HC1)  ?    What  weight  of  sulphide  would  be  required  ? 

1 7.  What  weight  of  nitrate  of  soda  contains  the  same  quantity 
of  nitrogen  as,  one  hundredweight  of  sulphate  of  ammonia,  (a) 
when   both   substances  are  pure,  (£)  when  the  former    contains 
8  per  cent,  of  common  salt  and  the  latter  3  per  cent,  of  moisture  ? 

1 8.  What  weight  of  bone  ash,  assumed  to  be  pure  calcium 
phosphate,  would  be  required  for  the  formation  of  one  hundred- 
weight of  super-phosphate  ?     What  weight  of  this  latter  material 
will  contain  100  Ibs.  of  phosphorus  pentoxide  ? 

19.  A  sample  of  soil — of  which  one  acre,  9  inches  deep,  weighed 
2-J-    million    pounds — was    found    to    contain  o'oi    per  cent,  of 
phosphorus  pentoxide  ;  what  quantity  of  phosphate  of  lime  (tri- 
calcic  orthophosphate)  per  acre  is  this  equivalent  to? 

20.  What  volume  of  gas  measured  at  150°  C.,  and  760  mm. 
pressure,  would  be  obtained  by  heating  10  grams  of  ammonium 
nitrate  ? 

21.  If  limestone  containing  90  per  cent,  of  calcium  carbonate 
cost,  say,  five  shillings  per  ton  at  the  quarry,  and  the  cost  of  carriage, 

2 


234  APPENDIX 

burning,  etc.,  amounted  to,  say,  ninepence  per  ton  of  limestone, 
at  what  price  per  ton  could  the  quicklime  be  sold  at  the  kiln, 
so  as  to  cover  expenses  ? 

22.  What  weight  of  caustic  potash  would  be  required  to  make 
one  ton  of  soft  soap,  assuming  that  it  was  made  from  palm  oil, 
and  that  this  was  pure  palmitin  ? 

23.  Potatoes  contain,  say,  18  per  cent,  of  starch.     What  weight 
of  glucose  could  be  obtained  from  three  hundredweight  of  such 
potatoes  ? 

24.  Five  grams  of  cheese  are  so  treated  that  all  its  nitrogen 
is  converted  into  ammonia.     If  it  is  found  that  from  the  ammonia 
so  liberated  ro6  grams  of  ammonium  sulphate  can  be  formed, 
calculate  the  percentage  of  nitrogen  in  the  cheese. 

25.  What  weight  of  common  salt  is  required  to  provide  sufficient 
chlorine  to  liberate  all  the  iodine  in  100  grams  of  a  10  per  cent, 
solution  of  potassium  iodide  ? 

26.  Fifty  cubic  centimetres  of  a  solution  of  hydrogen  peroxide 
were  found  to  liberate  0*3  grams  of  iodine  from  potassium  iodide 
in  the  presence  of  acid.     Calculate  the  percentage  of  hydrogen 
peroxide  in  its  solution. 

27.  What  weight  of  soda  crystals  can  be  theoretically  obtained 
from  one  pound  of  common  salt  ? 

28.  What  weight  of  wrought  iron  containing  0*8  per  cent,  of 
carbon  is  theoretically  obtainable  from  255   tons  of  haematite  free" 
from  impurities  ? 

29.  What  relative  quantities  of  cerussite  (PbCO3)  and  galena 
would  yield  equal  weights  of  red  lead  ? 

30.  Calculate  the  weight  of  the  residue  left  when  concentrated 
nitric  acid  acts  upon  5  grams  of  a  solder  containing  40  per  cent, 
of  lead  and  60  per  cent,  of  tin. 

31.  What  would  be  the  weight  of  the  solid  thrown  down  when 
5  grams  of  zinc  were  allowed  to  act  upon  excess  of  a  solution  of 
copper  sulphate  ? 

32.  A  certain  monobasic  acid  forms  a  silver  salt  containing 
63'53  per  cent,  of  silver.    What  is  the  molecular  weight  of  the  acid. 

33.  Find  the  number  of  grams  of  sulphuric  acid  (H2SO4)  in  a 
litre  of  a  solution  of  the  acid,   40  cubic   centimetres   of  which 
neutralise  2*92  grams  of  pure  sodium  carbonate.    What  volume 
of  hydrogen  at  N.T.P.  would  be  liberated  from  100  c.c.  of  the  acid 
by  the  action  of  zinc  ? 

34.  What  weight  of  calcium  carbonate  must  be  decomposed 
to  yield  sufficient  carbon  dioxide  to  convert  40  grams  of  sodium 
hydroxide  into  sodium  bi-carbonate  ? 


INDEX 


ABSORPTION  of  gases  by  charcoal, 

119 

Acetaldehyde,  150 
Acetamide,  184 
Acetanilide,  190 
Acetates,  154 

-,  action  of  heat  on,  154 

Acetone,  168 
Acetylene,  158 
Acid,  acetic,  152 

,  amino-acetic,  183 

• ,  amino-formic,  184 

,  arsenic,  214 

,  arsenious,  214 

,  benzoic,  190 

,  boracic  or  boric,  113 

,  butyric,  132 

,  carbonic,  69 

,  "carbolic,"  189 

,  carbamic,  184 

,  chloric,  77 

,  citric,  178 

,  formic,  152 

,  glycollic,  177 

,  hippuric,  190 

,  hydriodic,  79 

,  hydrobromic,  79 

,  hydrochloric,  78 

,  hydrocyanic,  179 

— ,  hypochlorous,  77 
,  hypophosphorous,  104 

— ,  lactic,  178 
,  linoleic,  166 

— ,  malic,  178 

• ,  malonic,  177 

•• ,  "muriatic,"  74 

,  nitric,  134 

,  nitrous,  137 

- — -,  oleic,  165 
,  oxalic,  176 


Acid,  palmitic,  165 

,  perchloric,  77 

,  ortho-phosphoric,  99 

— ,  meta-phosphoric,  99 
,  pyro-phosphoric,  100 

— ,  propionic,  152 

— ,  ricinoleic,  166 

— ,  salicylic,  191 

— ,  silicic,  1 06 

— ,  stearic,  165 

• ,  sulphuric,  88 

,  sulphuric,  fuming,  91 

,  tartaric,  178 

,  sulphurous,  87 

,  uric,  1 80 

Acidic  oxides,  53 
Acids,  53,60,  152 

,  basicity  of,  57 

,  liberation  of  hydrogen  from, 

,  dibasic  organic,  176 

,  properties  of,  53 

— ,  hydrony,  177 

,  organic,  152 

, dibasic,  176 

— , hydroxy,  177 

, tribasic,  178 

Addition  compounds,  157 
Adsorption,  119 
Aerated  waters,  28 
Air,  7 

,  density  of,  8 

,  composition  of,  9 

— ,  respired,  composition  of,  72 
Alabaster,  67 
Albumen,  183 
Albuminoid  ammonia,  30 
Albuminoids,  182 
Alcohol,  ethyl,  148 

, ,  action  of  sulphuric  acid 

upon,  156,  161 

— ,  methyl,  147 


236 


.INDEX 


Alcohols,  147 

,  oxidation  of,  149 

,  hexahydric,  170 

,  primary,  secondary  and  ter- 
tiary, 169 

,  polyhydricj  162 

»  a»yl>  155 

,  butyl,  149 

,  propyl,  149 

Aldehydes,  149 

Aldol,  151 

condensation,  151 

Alkali  metals,  192 

Alkaline  earths,  metals  of,  193 

Alkalis,  54 

Allotropy,  92 

Alloys,  216 

Aluminates,  195 

Aluminium,  194 

,  use  of,  for  cooking  utensils, 

196 

chloride,  78 

Alums,  195 

Amides,  184 

Amines,  182 

Amino-acetic  acid,  183 

Amino-benzene,  189 

Amino-formic  acid,  184 

Ammonia,  125 

,  albuminoid,  30 

,  composition  of,  126 

Ammonia-soda  process,  81 

Ammonium,  carbamate,  130 

,  carbonate,  130 

,  cyanate,  180 

,  formate,  134 

,  hydroxide,  127 

,  salts,  128 

, ,  action  of  heat  upon, 

129 

Amygdalin,  175 

Amyl  alcohol,  155 

acetate,  155 

Anhydrides,  87 

Aniline,  189 

Anode,  61 

Answer  to  numerical  examples,  244 

Anthracite,  120 

Anti-febrine,  190 

Antimony,  212 

,  alloys  of,  216 

,  hydride,  215 

Aqua-regia,  80,  211 

Aromatic  hydrocarbons,  188 

Arsenates,  214 


Arsenic,  214 

,  hydride,  215 

,  oxides  of,  214 

,  white,  214 

Arsenites,  214 
Asbestos,  109 
Ashes,  95 
Asparagine,  184 
Atmosphere,  the,  7 

,  the  chief  gases  of  the,  15 

Atomic  theory,  43 

weights,  44 

,  table  of,  217 

Atoms,  43 

Avogadro's  hypothesis,  75 


B 


Bacteria,  131 
Bacterium  aceti,  153 
Baking  powder,  81 
Barium,  193 

carbonate,  193 

oxide,  19 

peroxide,  19,  59 

sulphate,  193 

Barometer,  the,  12 
Barytes,  193 
Bases,  54,  60 
Basic  salts,  78 

slag,  198 

Basicity  of  acids,  57 
Bauxite,  196 
Bell  metal,  216 
Benzaldehyde,  190 
Benzene,  188 

,  action  of  sulphuric  acid  upon, 

1 88 

Benzine,  188 
Benzoic  acid,  190 
Benzoline,  140 

benzylalcohol,  190 

"  Biscuit,"  porcelain,  no 
Bismuth,  212 
Black  ash,  81 

lead,  122 

Bleaching,  60,  76,  87,  114 

powder,  77 

Blende,  204 

Boiler  "fur,"  70 

Bone  ash,  97 

Bones,  9? 

Boracic  or  boric  acid,  113 

Borate  of  manganese,  202 


INDEX 


237 


Borate  pyro.  of  sodium,  113 

per.  of  sodium,  114 

Borax,  113 

Bordeaux  mixture,  207 

Boric  acid,  113 

— ,  tests  for,  114 
Boric  anhydride,  114 
Boron,  113 
Boyle's  law,  1 1 
Brass,  216 
Bromine,  79 
Bronze,  216 

,  aluminium,  216 

Bunsen  flame,  the,  161 
Butane,  141 


Cadmium,  205 

,  yellow,  205 

Calcite,  64 
Calcium,  193 
—  carbonate,  64 

occurrence  in  nature,  64 

—  bi-carbonate,  69 

carbide,  68 

chloride,  67 

oxide,  65 

phosphates,  103 

silicate,  66,  in 

sulphates,  67 

Calculation,  problems  for,  232 
Calculations,  45 
Caliche,  132 
Calomel,  210 
Cane  sugar,  172 
Carbamic  acid,  184 
Carbamide,  125,  180 
Carbohydrates,  170 
"  Carbolic  "  acid,  189 
Carbon,  122 

-,  heat  of  combustion  of,  1 7 

compounds,  181 

•,  reducing  action  of,  123 

assimilation  by  plants,  151 

,  valency  of,  143 

monoxide,  123 

dioxide,  68 

Carbonates,  72 
Carbonic  acid,  163 

anhydride,  69 

Carbonyl  compounds,  97,  125 

chloride,  125 

nickel,  125 


Carborundum,  m 

Carnallite,  95 

Casein,  21,  184,  1 86 

Catalysis,  134 

Caustic  "  Lunar,"  21 1 

Celluloid,  174 

Cellulose,  173 

Cement,  67 

Centigrade  thermometer  scale,  13 

Chalk,  64 

Changes,  physical,  2 

,  chemical,  3 

Charcoal,    animal    and   vegetable, 
119 

,  absorption  of  gases  by,  119 

,  filters,  119 

Charles's  Law,  II 
Chemical  change,  3 
Chemical  combination,  3 

,  laws  of,  40 

nomenclature,  37 

Chemistry,  quantitative  nature  of, 

45 

Chili  saltpetre,  133 
China-clay,  105 
Chlorates,  19,  77 
,  preparation  of  oxygen  from, 

19 

Chloride  of  lime,  77 

• calcium,  67 

Chlorides,  78 
Chlorine,  74,  76 

,  bleaching  action  of,  76 

action  on  unsaturated  hydro- 
carbons, 157 
Chloroform,  145 

Chlor-substitution  compounds,  145 
Chromates,  204 
Chrome  alums,  195 

,  yellow,  209 

Chromium,  203 

,  oxides  of,  203 

Chromic  salts,  204 
Chromous  salts,  203 
Cinnabar,  210 
Clay,  105 

iron  ore,  196 

Coal,  120 

-,    destructive    distillation     of, 

121 

gas,  121      * 

tar,  121,  187 

Cobalt,  203 

Cobaltous  salts,  colours  of,  203 

Coke,  J2i 


INDEX 


Colloids,  107 

Combination,  laws  of  chemical,  40 

Combustion,  16 

,  heat  of,  17 

,  slow,  1 8 

— '— ,  supporter  of,  16 

Common  salt,  73 

Composition,  calculation  of  per- 
centage, 46 

Composts,  131 

Compounds  and  mixtures,  5 

Condy's  fluid,  202 

Conservation  of  matter,  law  of,  48 

Copper,  205 

Copper  pyrites,  205 

Coprolite,  100,  103 

Corrosive  sublimate,  210 

Corundum,  194 

Critical  pressure,  71 

temperature,  71 

Crocus  martis,  200 

Crystallisation,  water  of,  29 

Crystalloids,  107 

Crystals,  29 

Cupric  salts,  206 

Cuprite,  205 

Cuprous  salts,  206 

chloride,  preparation  of,  207 

Cyanate  of  ammonium,  action  of 
heat  upon,  180 

Cyanates,  180 

Cyanide  of  potassium,  reducing 
action  of,  180 

mercuric,  action  of  heat  upon, 

179 

Cyanides,  179 

Cyanogen  gas,  179 


D 

Decay,  131 
Decomposition,  4 

,  double,  49 

Definite  proportion,  law  of,  40 
Deliquescence,  29 
Dextrin,  173 
Dialysis,  107 
Diamond,  123 
Diastase,  173      0 
Dionaea,  22 
Dissociation,  129 

,  ionic,  60 

Distillation,  23 


Distillation,  destructive,  118 
Dolomite    (magnesian    limestone), 

193 
Drosera,  22 


Earth  metals,  194 
Efflorescence,  29 
Electrification,  3 
Electrodes,  61 
Electrolysis,  31,  6 1 
Elements,  5 
Emerald  green,  207 
Energy,  I 
Enstatite,  108 
Enzymes,  174 
Equations,  48 
Equivalents,  42 
Essences  fruit,  155 
Esters,  154 
Ethane,  141 
Ethereal  salts,  154 
Ethers,  161 
Ethyl  alcohol,  148 

,  action  of  sulphuric  acid 

upon,  156,  158 

,  commercial  preparation 

of,  174 

Ethylene,  156 
,  dichloride,  157 


Fahrenheit's  thermometer  scale,  13 

Fats,  165 

Fehling's  solution,  171 

Felspar,  109 

Fermentation,  174 

,  alcoholic,  174 

,  butyric  acid,  174 

,  lactic  acid,  174 

Ferric  salts,  200 
Ferrous  salts,  200 
Fire-damp,  139 
Flame,  structure  of,  159 

,  the  Bunsen,  161 

Flash  point  of  lamp  oils,  142 

Flesh,  21,  184 

Fluorides,  112 

Fluorine,  112 

Food,  animal  and  plant,  21 


INDEX 


239 


Food,  preservatives,  73,   114,  150, 

191 

Force,  2 

Formaldehyde,  150 
Formalin,  150 
Formic  acid,  152 
Formose,  152 
Formulae,  44 
,   calculation  from   results   of 

analysis,  47 
Fructose,  171 
Fruit  essences,  155 

sugar,  171 

Fuels,  142 
Fungicide,  3,  207 
M  Fur"  boiler,  70 
"  Fusel  oil,"  155 


Galactose,  171 

Galena,  208 

Gas,  illuminating,  121 

,  water,  124 

mantles,  incandescent,  159 

Gases,  general  properties  of,  10 

,  liquefaction  of,  71 

Gay-Lussac  tower,  89 
German  silver,  216 
Glass,  in 

,  action  of  alkalis  upon,  1 1 1 

,  action  of    hydrofluoric    acid 

upon,  112 

Glasses,  coloured,  in 
Glauber's  salt,  82 
Glover  tower,  89 
Glucose,  171 
— — ,  tests  for,  172 
Glucosides,  175 
Gluten,  21 
Glycerides,  165 
Glycerine,  164 
Glycerol,  164 
Glycine,  184 
Glycocine,  184 
Glycocoll,  184 
Glycol,  163 
Gly collie  acid,  177 
Gold,  211 
,  chloride,  action  of  heat  upon, 

212 

Graphite,  122 

Green,  emerald  or  Paris,  207 

,  Scheele's,  207 


Gun-cotton,  174 

metal,  216 

Gypsum,  67 


II 


Halogens,  the,  79 

Hardness  in  water,  69 

,  temporary,  70 

,  permanent,  7 1 

,  methods  of  removing,  70 

Hard  water,  action  on  soap,  69, 
167 

Heavy  metals,  192 

—  spar,  193 

Homologous  series,  141 

Hydrocarbons,  paraffins,  141 

,  defines,  156 

,  aromatic,  188 

Hydrochloric  acid,  74,  78 

,  composition  of,  75 

- ,  oxidation  of,  79 

,  action  of  metals  on,  78 

Hydrocyanic  acid,  179 

Hydrogen,  preparation  and  pro- 
perties of,  32 

,  as  a  reducing  agent,  34 

,  peroxide,  59 

Hydrolysis,  78 

Hydroxides,  54 

Hydroxyl  derivatives  of  hydro- 
carbons, 146 

"Hypo,  "82 

Hypochlorous  acid,  77 

Hypophosphorous  acid,  104 


Ice,  2 

,  commercial    preparation    of, 

128 

Iceland  spar,  64 
Incandescent  gas  mantles,  159 
Indican,  175 
Indigo,  175 
Indoxyl,  175 
Ink,  199 
Insecticides,  191 
Iodine,  79 
Ions,  6 1 
Iron,  196 

,  smelting  of,  196 

,  cast,  197 


240 


INDEX 


Iron,  rust,  198 

,  wrought,  197 

Isomerism,  167 


K 


Kainite,  96 
Kaolin,  105 
Kaolinite,  109 
Kathode,  61 


Lactose,  172 
"Lakes,"  195 
Lamp  oils,  142 
Lapis-lazuli,  III 
Law,  natural,  40 
Lead,  207 

• ,  action  of  water  upon,  208 

• ,  oxides  of,  208 

paints,  blackening  of,  209 

pipes  for  water  supply,  208 

poisoning,  208 

Le  Blanc  process  for  manufacture  of 

soda  crystals,  81 
Leguminosre      and      atmospheric 

nitrogen,  the,  22 
Light,  action  on  silver  salts,  211 
Lignite,  120 
Lime,  66 

burning,  64 

,  the  slaking  of,  66 

Limelight,  159 
Limestone,  64 
Litmus,  9,  54 
Lubricating  oils,  143 


M 

Magnesia,  194 
Magnesian  limestone,  193 
Magnesium,  193 

chloride,  193 

nitride,  193 

silicide,  106 

sulphate,  194 

Magnetisation,  3 
Malachite,  205 
Malic  acid,  178 
Maltose,  172 
Manganates,  201 


Manganese,  201 

,  oxides  of,  201 

borate,  202 

Manganic  salts,  201 
Manganous  salts,  201 
Marble,  64 
Marriotte's  law,  II 
Marsh  gas,  139 
Mass,  2 
Matter,  properties  of,  I 

,  three  states  of,  3 

Meerschaum,  109 

Mercuric  oxide,  18,  210 

Mercury,  210 

Metals,  192 

Methane,  141 

Methyl  alcohol,  147 

Methylamine,  182 

Methylated  spirit,  149 

Mica,  109 

Microcosraic  salt,  101 

Minium,  209 

Mirbane,  oil  of,  189 

Mixtures,  5 

Molasses,  96 

Molecular  weight,  45 

Molecules,  43,  75 

Mordants,  195 

Mortar,  66 

Multiple  proportion,  law  of,  42 

Muriatic  acid,  74 

Mycoderma  aceti,  153 


N 


Naphthalene,  191 
Natural  law,  40 
Nepenthes  (Pitcher  plant),  22 
Neutralisation,  54 
Nickel,  203 

carbonyl,  125 

Nitrate    of   ammonium,    action   of 

heat  on,  129 
Nitrates  of  metals,  136 

-,  action  of  heat  upon,  136 

Nitre,  132 
Nitric  acid,  134 

,  action  upon  metals,  136 

oxide,  137 

Nitrides,  133 

Nitrification,  131 

Nitriles,  181 

Nitrites,  137 

and  nitrates  in  water,  137 


INDEX 


Nitrobenzene,  189 
Nitrogen,     preparation    and     pro- 
perties, 21 

— ,  atmospheric,  fixation  of,  132 
,  relation   to  animal  and 


vegetable  life,  2 1 
-,  excretion  of,  180 


tis- 


in  animal  and  vegetable 

sues,  117 
— ,  oxides  of,  137 
Nitrogenous  foods,  21 
— —  organic  compounds,  179 
Nitrous  acid,  137 

• oxide,  137 

Noble  Metals,  the,  210 
Nomenclature,  37 
Normal  salts,  57 
Notation,  symbolic,  39 


O 

Oil  of  bitter  almonds,  190 

•  mirbane,  189 

—  wintergreen,  191 
—  vitriol,  91 

,  mineral,  139 

— ,  paraffin,  142 
— ,  vegetable  and  animal,  165 
Oils,  drying,  166 
— ,  lamp,  142 

,  lubricating,  143 

Olefiant  gas,  158 

Olefines,  156 

Olein,  165 

Olivine,  108 

Ores,  196 

Organic  matter,  117 

Orthoclase,  109 

Orthophosphates,     effect    of    heat 

upon,  1 02 

Orthophosphoric  acid,  ioo 
Orthosilicic  acid,  108 
Osmotic  pressure,  114 
Oxide  of  barium,  19,  193 
Oxides,  S3 

acidic,  53 

classification  of,  59 
basic,  54 
per,  58 
Oxygen,  15 

commercial  preparation  of,  19 
relation    to    respiration    and 
combustion,  20 
Oxymuriatic  acid,  76 


Ozokerite,  143 
Ozone,  93 


Paints,  white,  193,  205,  209 

Palmitin,  165 

Paper,  173 

Paraffin  hydrocarbons,  139 

,  oils  and  waxes,  143 

Passive  state,  203 

Pearl  ashes,  95 

Pearls,  64 

Peat,  120 

Pentane,  141 

Perborate  of  sodium,  114 

Percentage  composition,  calculation 

of,  45 

Peridot,  1 08 
Permanganates,  202 
Peroxide  of  hydrogen,  59 
Peroxides,  58 
Petrol,  140 
Petroleum,  139 
Pewter,  216 
Phenol,  189 
Phosphates,  ioo 
Phosphine,  104 
Phosphonium  compounds,  104 
Phosphoretted  hydrogen,  104 
Phosphoric  acids,  99 

,  anhydride,  99 

Phosphorous  acid,  104 

Phosphorus,  98 

Pigments,  201 

Pitcher  plants,  22 

Plant-life,  relation  of  atmosphere  to, 

21,   151 

Plants,  carnivorous,  22 
Plaster  of  paris,  67 

,  lead,  167 

Platinum,  212 

,  chloride,  action  of  heat  upon, 

212 

Plumbago,  122 
Polyhydric  alcohols,  162 
Polymerism,  170 
Potashes,  95 
Potassium,  97,  193 

,  carbonate,  96 

,  ferrocyanide,  179 

— — ,  permanganate,  202 
Pottery  and  porcelain,  no 
Preservatives,  73,  114,  150,  191 


242 


INDEX 


Pressure,  critical,  71 

,  atmospheric,  measurement  of, 

12 

,  osmotic,  114 

,  relation  to  volume  of  gases,  1 1 

,  atmospheric,  12 

Priestley,  15 
Propane,  141 
Proteids,  184 
Prussian  blue,  201 
Prussic  acid,  180 
Putrefaction,  130 
Pyrites,  copper,  205 

,  iron,  88 

Pyroligneous  acid,  118 
Pyrolusite,  201 
Pyrosulphuric  acid,  91 


Quantitative  nature  of  chemistry, 

45 

Quartz,  105 
Quick  lime,  66 

R 

Reaumur's  thermometer  scale,  13 
Red  lead,  209 
Reducing  agents,  34 

agent,  hydrogen  as  a,  35 

,  carbon  as  a,  123 

sugars,  171 

Reduction,  35,  87,  123 
Respired  air,  composition  of,  72 
Reversible  reactions,  65 
Rock  oil,  139 
Rouge,  jewellers,  200 
Rusting  of  iron,  17 


Sal-ammoniac,  127 
Salicin,  175 
Salt  cake,  81 
Salt,  common,  73 
Salt,  Glauber's  82 
Salt  glaze,  1 10 
Salt,  microcosmic,  101 
Saltpetre,  132 

,  Chili,  132 

Salt,  spirit  of,  73 
Salts,  54,  60 

,  normal,  57 

,  of  sorrel,  171,  199 


Sand,  105 

Saponin,  176 

Saturated  compound,  145 

Scheele,  15 

Series,  homologous,  141 

Serpentine,  109 

Shot  or  bullet  metal,  216 

Silica,  106 

,  soluble,  107 

Silicic  acids,  106 
Silver,  210 

,  blackening  of,  211 

Silver  salts,  action  of  light  on,  211 
Slag,  196 

,  basic,  198 

Slaked  lime,  66 

Smalt,  203 

Soap,  action  of  hard  water  on,  69, 

167 

Soaps,  165 
Soda,  caustic,  82 

,  crystals,  81 

Sodium  80, 

carbonate,  8l 

bicarbonate,  82 

chloride,  73 

hydroxide,  82 

nitrate,  82 

silicate,  106 

sulphate,  82 

thiosulphate,  82 
Softening  of  water,  70 
Solutions,  26 
Solder,  216 
Solubility  curves,  27 
Solvay  process,  81 
Solvent,  water  as  a,  26 

,  alcohol  as  a,  148 

Spirit  of  hartshorn,  120 

salt,  73 

wine,  148 

lamps,  148 

Starch,  173 

,  hydrolysis  of,  173 

Stassfurt  salt  deposits,  96 
State,  change  of,  3 
Stearin,  165 
Steel,  196 

,  tempering  of,  198 

Stuffiness  of  rooms,  72 
Substitution  compounds,  145 
Sugar-beet,  172 
Sugars,  170 
Suint,  96 
Sulphates,  83 


INDEX 


243 


Sulphides,  83 
Sulphites,  88 

Sulphur,  occurrence   and   purifica- 
tion, 83 
Sulphur,  allotropic  forms  of,  84 

,  dioxide,  85 

, ,  composition  of,  86 

,  trioxides,  88 

Sulphuretted  hydrogen,  91 
Sulphuric  acid,  88 

anhydride,  88 

acid,  fuming,  91 

Sulphurous  acid,  87 

anhydride,  87 

Sundew,  22 
Superphosphate,  102 
Sylvite,  95 

Symbolic  notation,  39 
Symbols,  39 


Talc,  1 10 
Tar,  coal,  186 

,  wood  (Stockholm  tar),  Il8 

Temperature,  12 

,  absolute,  1 1 

,  critical,  71 

,  relation  to  gaseous  volume,  n 

Thermometer  scales,  13 
Thermometers,  13 
Tin,  211 

,  action  of  nitric  acid  on,  135 

Tincal, 
Toluene,  188 
Turmeric,  114 
Turpentine,  76,  93 
Type  metal,  216 


U 


Ultramarine,  HI 
Unsaturated  hydrocarbons,  157 
Urea,  180 
Uric  acid,  180 
Urine,  180 


Valency,  50 
Vaseline,  143 
Venetian  red,  200 
Verdigris,  207 
Venus'  fly  trap,  22 
Vinegar,  154 


Vitriol,  oil  of,  91 
Vitriols,  201,  205,  206 
Volume     of     gases,    relation   to 
temperature  and  pressure,  1 1 

W 

Washing  soda,  81 
Water,  23 

,  physical  properties  of,  25 

,  solvent  properties  of,  26 

— ,  solubility  of  solids  in,  26 

,       ,,        ,,       gases  in,  28 

,       ,,        ,,       liquids  in,  28 

,  hard,  69 

,     „     methods  of  softening,  70 

,  drinking,  30 

,  composition  of,  31 

,  electrolysis  of,  31,  60 

,  purification  of,  23,  24 

,  action  of  metals  on,  32 

Water  glass,  106 
Waters,  natural,  29 
Waxes,  156 
Weight,  2 
Welding,  197 
White  lead,  209 
White  paints,  193,  205,  209 
Wintergreen,  oil  of,  191 
Witherite,  193 
Woad,   175 
Wollastonite,  108 
Wood,  117 

•  ashes,  95 

,  dry  distillation  of,  118 

—  spirit,  u  8,  147 
Writing  ink,  199 


X 


Xylene,  188 


Yeast,  174 

action  upon  sugars,  1 74 

enzymes  present  in,  185 


Zinc,  204 

Zinc  chloride,  78 

oxide,  205 

sulphide,  205 

Zincates,  205 
Zymase,i75 


ANSWERS 

1.  ii'99-  2.  32-65. 

3.  (i)  K     24-68.     (2)  C  42-11.     (3)  Fe     20-14.     (4)  Na  21-59 

Mn  34-81.  H    6-43.  S       11-51.  Cl   33-34. 

O     40-50.          O  51-45.  O      23-02.  O    45*07. 

H20  45*33. 

4.  (i)  C6H5NO^  Nitro-benzene. 

(2)  Na2SO4ioH2O,  Glauber  salt. 

(3)  K2S2O7,  Potassium  pyrosulphate. 

(4)  K4FeCGN6,  Prussian  blue. 

5-  5!3'947  c.c.  6.  io'8°  C. 

7.  128-1  mm.  increase.          8.  I7o5.mm.,  i.e.  2*24  atmospheres. 
9.  2-5 59  litres.  10.  u  grams. 

11.  54*54  per  cent.  12.  84  grams. 

13.  7-768  grams. 

14.  CuO  79*5  grams,  CuSO45H2O  249-4  grams. 

15.  5-89  litres.  16.  1*83  litres  H2S,  7*225  grams  FeS. 
17.  (a)  144-2  Ibs. ;  (£)  152-1  Ibs.     18.  (a)  68'6i  Ibs. ;  (£)  356-6  Ibs, 

19.  545-8  Ibs. 

20.  13-01    litres,  of  which  one-third  is  nitrous  oxide,  and  two- 
thirds  water  vapour. 

21.  1 1 s.  4'6d.  per  ton.  22.  426-72  Ibs. 
23.  67-2  Ibs.  24.  4-498  per  cent. 
25.  3*526  grams.  26.  0-0598  per  cent. 
27.  2-448  Ibs.  28.  1 79-956  tons. 
29.  267  :  239  by  weight.  30.  SnO2  3'8  grams. 
31.  4-879  grams  Cu.  32.  62-8. 

33.  67*49  grams  ;  13*842  litres.     34.  100  grams. 


THE    END 


PRINTED    1JY   WILLIAM   CLOWES   AND   SONS,    LIMITED,    LONDON    AND   BECCLESv 


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